Going down the responses a bit
First of all, the reason why they live on Targon is a tricky question to answer. For example, there are the Eskimo who live in the tundra, why do they live there? You (hypothetical you) could argue that hey just do. Free living space is a commodity, and if you have no home, you end up raiders, people with no place to call home who are desperate enough to go anywhere.
Oh I have no problem with them living on Targon. People live in a lot of inhospitable areas and have adapted to live there very well. People live next to volcanoes (actually usually that's a really good place to live, very fertile, except for the eruption thing), people live on the equator and in the arctic. Usually, because their ancestor's lived there, and decided not to move (or perhaps they were moving and decided to stay) for whatever reason. Perhaps a good source of water, or perhaps it was just the closest livable location from the last livable location until they end up winding up in whatever area they are in.
But here's the thing, no one raided the Eskimo villages. Some have tried to conquer it. Other Eskimos might raid their neighbors. But no one traveled by ship to the frozen north saw a bunch of people living in poverty and thought "yeah, this is a trip that's worth taking again, and again."
Examining Targon, we see a rough mountain with evil spirits but great power. I think that it's the rumors and tales of this great power that draws desperate gloryhounds and adventurers alike to the mountain. Some choose to simply climb it, and die in the process. The raiders perhaps believe that by ransacking the tribes they will find riches or something of power.
And when they go back home and tell everyone "well there's no riches there, that was a bunch of bull" then the raiding would stop. Or, when the Rakkor, who still seem to be very competent fighters kill all the raiders and there are no more messages back home then the raiding would also stop.
Now, the two historical reason for raiding in inhospitable lands is if you're trying to colonize and are being pushed out of your land for whatever reason, perhaps it became more inhospitable, perhaps your lands were conquered, whatever. However, the raiders we've seen haven't been migratory. So that's out. The other possibility is slavery, however again, we haven't seen them actually even try to take slaves, and said Rakkor seem adept at killing the raiders, so, again, that'd be a horrible place to get your slaves.
And in actuality, I think the Rakkor just aren't very Spartan anymore. The Spartans lived in Sparta, a city, there were hundreds of thousands at any one time. Also, the Spartans made use d slaves (I believe they conquered another city state) to do all the necessary things like farm and labor so the true blooded Spartans could focus on war. To the Spartans, war was something of a divine right, a glorious cause and they leapt at any chance they could get.
Rakkor is exactly as Spartan as Riot wants them to be. It started out as very 'Hollywood' Sparta, during Leona's release it was turned into 'Stupid Hollywood' Sparta (really, making the kids kill each other, effectively halving your population? No one's done that outside of bad teen angst sci fi).
You are right that the Spartans were not all warm and cuddly and honorable (well, they would disagree on that last one, but the ancient Greek perception of honor and our own modern variations is wildly different).
But hell, even if you wanted to tone down the slavery aspects of Sparta to make Leona seem nice, you could easily show Sparta as the warrior tribe of the Rakkor tasked with protecting the others. Hell, the Spartans themselves thought of themselves as the Guardians of the Hellenes. For while this was actually recognized, legally, in the Greek city-states. Only now you say the tribute was food and supplies to keep up their warrior lineage unperturbed. Done.
How many Rakkor are there? Not nearly as many. They are a tribe, so at the most a few thousand, and that's quite possible overestimating depending on how a tribe is defined. My point being is that the Rakkor can't expend the resources to travel to faraway lands to fight wars for gods and cities they don't hold allegiance to. They are not a warrior race, they are fighters because to live on Targon is to fight for survival, and a tribe not willing to stand up for itself will soon die.
Again, as many Rakkor as Riot says there are. It's a mountain whose actual size is never said, besides "ginormous" the Rakkor tribe could be any size that Riot says. Hell, it could have been made into a bunch of smaller tribes to band together during large wars. This is actually in itself vaguely Spartan-esque as the Spartans were really from 4 cities that combined together were called the Lakedaemons (which is why the Spartan's had the lambda on their shields).
If we just take Mount Everest as a basis, there are currently 40,000 people living on it. Sparta at it's height was thought to be 20,000 true Sparitiates, and 40-50,000 helots (serf-slaves), and periokoi (non-city dwellers). But this dwindled dramatically, to half that number a couple hundred years later. Well within the scope of a mountain society living on a mountain that dwarfs Everest. And hell, you could add details like that into Pantheon's personality if you want. Imagine if he was trying to find a way to balance the past traditions that made the Rakkor what they were, while their society is so obviously less than what it was. That could make an interesting story right there.
The Rakkor have animals and farms to tend to. They have to survive first, fight later. Imagine the shame you would bring to your family if you as a Rakkor left the tribe to journey abroad. You'd be despised and resented, you'd be seen as abandoning your people and sacred homeland.
No, that's not in the Lore at all like this. In fact it seems a common thing for the Rakkor people to climb up a mountain so dangerous that it's tantamount to suicide, and there was nothing about Pylas and Atreus being hated for abandoning their tribe.
As to farming and animals. The society is again, set up exactly like Riot wants. This could easily be worked around, hell, I worked around it a few paragraphs up already. It was only a limiting factor because that's the way Riot decided to go with the lore, I just disagree that what we ended up getting was the best they could have done. But I'll admit my biases right here. I love history. I love complex societies. I love human drama of warring civilizations and what makes empires rise and fall. I love politics and people struggling with social change. And I am bored to tears as soon as godly powered aliens suddenly get involved.
As for resources, why would, the Noxians for instance hire a bunch of angry hicks who speak a weird language when they have their own armies instead? We have no idea what kind of equipment the Rakkor are packing, since Pantheon and Leona wear armor forged by the Targonians.
Well, in the original lore, 1 Stanpar/Rakkor soldier was worth 10 Noxian and Demacian. That's why you'd want to hire them. And, if you have the money, why not. Rome's army ran on hiring yokels to do their fighting for them, even when they had a very powerful army themselves. Being able to open their purse and just hire fully trained warriors, even if they're not as disciplined as their usual troops (speaking of the barbarian mercenaries the Roman's used here) saves time, resources, and can provide much needed diversity in your army.
If you want mercenaries, go with something like a Freljordian berserker or a Shuriman. The Rakkor don't seem to be a people who would expend valuable resources (people) to fight for something like money. The Rakkor don't have he leisure time or the resources to send capable bodies abroad when they are clearly needed at home.
Mercenaries was just one means of getting the Rakkor fighting in massive wars. There are plenty of others, from a civil war amongst themselves (perhaps over a grand change in their religion, wink wink, nudge nudge, Diana and Leona, say no more), perhaps their position of prominence among the Mount Targon tribes is up for grabs. Perhaps there is an actual reason for Demacia or Noxus to try and conquer them in the Rune Wars, or whatever other conflict you can have in LoL background history. Humanity has been killing each other for our entire recorded history. If Riot wanted they could have found amazing reasons.
But in the end, they didn't want to. They didn't want to focus on a warrior culture, they didn't want to examine the life of someone taken from their families at age 7 and forced to become a soldier, they didn't want to focus on the complex hegemonies over power and war.
And I can't fault them for that, it's their story. They can tell it however they want. And they chose to instead focus on a race of body snatching aliens. It perplexes me that they went this route. I don't like that they went this route. In fact I think it's kind of stupid. But it's their game, their story, and besides make overly long and boring posts (sorry about that by the way) I can't really influence their opinion. What am I gonna do, say I quit LoL? They won't even notice I'm gone. I'll stay, keep playing my favorite champion, pretending he's still the Spartan he once was. Up until they do that visual work over they said was going to be somewhere far down the line. When he bears no resemblance to my Pantheon, then I'll probably be gone and that will be that.
