like i get energy where casting like 3 consecutive skills makes you go out of energy, but what about riven, kat, garen? it just seems kinda wtf to make them not have to worry about going oom or not having energy like every other champ in the game. is it supposed to compensate for something like high spell cds?
btw im not salty im just curious
Katarina - Low base damages, weak laning phase, easily cancellable ultimate, no CC
Riven - No ranged wave-clear or poke, reliant on snowballing, needs to be in melee range to do anything, CC (silence, snare, suppression, polymorph, entangle, stun)
Garen - Entirely melee range, low mobility, no CC (aside from a Silence) to help stick on targets, very predictable and can be easily kited in teamfights.
All of the champs that are resource less are shutdown hard with CC.
what makes being manaless balanced?
Mostly it has to do with this:
Generally speaking, you'll find the vast majority of manaless champions are in a wierd gray area when it comes to their abilities feeling more like auto-attacks than anything else.
By and large, manaless champions also aren't front-loaded.
Which subsequently ends up being a matter of a few seconds when comparing pure-AA power and pure burst come late game via the opposite ends of the spectrum in:
vs. 
.
Early game the difference between fighting those 2 is pretty substantial though, and it's worth considering mana just stops mattering come late-game for all but ~4 champions as per-level MP and MP/5 bonuses are pretty considerable and end-game is less about a 10 minute endurance run and more about picking the right team fights.
But look at the vast majority of manaless champions and you'll see their manaless abilities function more like auto-attack steroids over anything else.
Take 
for instance:
Each hit of Broken Wings does less damage than 1 of her auto-attacks at rank 1 or when she has at least 225 AD with rank 5 before factoring in her passive (in which case 1 of her AA's will often do double the damage of Broken Wings).
Read the skill as burst and it seems impressive, but when you consider it's 3 separate hits it's much more in line with just being an interesting %AS steroid over anything else.
Sure there's animation canceling, but even with perfect skills in that - Riven isn't going to match the single-hit to apply everything in QWE that a fighter/assassin like 
or 
can cause to happen.
With Riven there's always the chance to sort-of screw up her combo by landing that slow cast CC and locking her out of hit 3, where with Fizz/Jax it's just 100% of their combo and Tri-Force landing before any CC can even slow them down as a trade-off for having mana costs.
No idea what the tradeoff for 
is in why they don't use mana, but for everyone else that's manaless there's a pretty heavy lean into using sustained-DPS sudo-attack abilities like 
's Spin to Win or 
's Flame Spitter over front-loading everything.
Especially if you take into account what archetype a champion belongs to. 
is going to take more time landing a kill than 
because heavy burst isn't a core feature of fighters while it is pretty core to assassins, but both take more time to land a kill than comperable mana-users like 
or
"In general", manaless champions are gated by having large cooldowns. This is further exasperated by many CDR items having some sort of resource component.
Personally, I think it would make better sense if all champions had some sort of resource, even if it's not mana or energy. For example, If Vladimer had a visible Blood meter, where you could only pool if it was full (like a Shyvana R or Aatrox Passive), that would provide meaningful counterplay - You don't have to hope you can do math in your head to when it's available. Even if ALL IT DOES is show when the ability is off cooldown, that changes how the champion plays. But, once the resource is in place, that is a lever you can use to balance the champion as well (for example, the more blood you have, the lower the Q heals, or the lower his regeneration from E is). Likewise....
I can't think of reasoning for all of them, but I can take a stab at a couple:
Heavily based on resets, ideally will use her entire basic kit 3+ times in a team fight, even possibly a second ult. For this reason, energy isn't advised, as she'd need ridiculous amounts of energy restoration (to the point where giving her energy would basically be pointless anyway). At the same time, she has a weak laning phase which is typically pretty easily abused, and mana restrictions would make things much more difficult for her on top of that. Many times Kat has nothing to do in lane other than desperately try to CS with Q and if she could run out of mana then that'd shut her down even more. Basically neither mana nor energy make sense on her.
Kinda similar to Kat. Too spammy to use energy, arguably too spammy even to support mana. Honestly not certain she couldn't survive on mana to be honest, I can't be sure.
No idea at all. He's not super spammy to the point where he couldn't avoid running OOM constantly, he doesn't use lots of low CD abilities so he would have no problems with energy and unlike Kat, his laning phase is actually very strong for a top laner. Pretty sure this is just "lol Garen needs to be easy". He'd have no problems whatsoever if he ran off mana, and I doubt Garen mains would really care if he did to be honest. I guess the best argument I could see for him not having mana is that he's supposed to stay on the map as long as possible due to his passive, but eh.
