I first want to say that I totally agree with pretty much everything you are saying. I agree that the game is a touch too snowball, and that the window for certain roles to have agency need to be adjusted.
Let me give you a scenario that happens often and I think illustrates our point perfectly. I play ADC, I go 3-0-1 in lane and my support goes 1-0-3. At the start of the game my Lee Sin jungle invaded their Xin jungle and stole his second buff, burned his flash, and sent him back to base at lvl 2. Lee Sin now thinks he is God and keeps invading even when our mid is pushed in and with limited vision, as a result Lee's amazing start has now resulted in Xin being 1-0-2 and their mid being 2-0-1. You know who is great at killing adc's? Xin and mid laners. Despite the fact that my stats are individually better than either of their players with kills, despite the fact we have 4 kills including first blood and they have 3, we are on the back foot because Xin can dive me at will and mid can blast me super hard so I can't abuse the advantage I've created and snowball further. This is further exasperated by the fact that it's far easier for mid and jungle to gank bot than for adc and support to gank mid or jungle successfully.
Again I think some adjustment has to be made, but here is some insight into why the throw has to be stronger than the carry. I am a big fan of Esports in general, so while I pretty much play LOL exclusively, I watch all competitive gaming including Dota 2. Dota 2 is the closest thing out there to LOL right now, and there is a reason why it is less popular. Casual players typically want to end games quickly and they want to kill stuff way more than playing the map or waiting for timings. In Dota a support feeding their face off is not that impactful and sometimes is actually good (they call it tanking the gank); the support will know that the enemy team is looking to make a play soon, so they start roaming around and playing super ballsy in neutral areas and the jungle like "I'm way overextended and yeah you would rather gank my carry down there in lane but the kill on me is so easy and by the way if you don't kill me I'm gonna take your rune and kill one of the only 3 wards you have up on the map". They also have certain carries who can just carry the game so that like if 4 players are slowly losing the game and losing skirmishes, your 1 player farming that whole time can realistically carry the game. The game ha a rubberband effect more than a snowball. The games last longer because it's truly not over until the fat lady sings, and I've seen multiple games where a team has mega creeps pushing in from all 3 lanes and the opponent still has 2/3 tier 2 towers up, yet somehow they pull out a comeback. Something like that would be like legendary status in LOL, like the Xpeke backdoor, in Dota it happens often enough that a lot of them aren't really talked about much after the week it happens.
Finally making my point: LOL is largely successful because it is more friendly towards casual players than something like Dota is, but feels more involved and more competitive than something like HOTS. This is why Riot typically trends more towards buffing underpowered things up to par with OP stuff than just nerfing the OP back into line with everything else. Once a player has had the chance to feel that power in their hands, they will cry like a little 2 year old if you remove some of that agency you talked about. Casual players get bored with long games, they get frustrated more easily (meaning if they lose a fight after winning several early they will cry), and they want to fight a lot, they also want to feel like the hero. If you tell people, "Hey you just constantly fighting and roaming for kills is not gonna win you the game most of the time, snowballing through your lane and split pushing isn't gonna be much better", it will significantly impact the involvement of casual players.
Riot does their best to balance around both team oriented play and "yolo q" playstyle, but the attitude that the came can and should be mostly decided in the first 20 minutes will continue to edge out because it's easier to do so in anything but arranged 5's and because it's less frustrating to casuals. If a mid tier casual player continually fights in lane and ends up 1-3 and down 30 cs with lost tower they are the one spamming surrender and ready to give up, they may lash out saying they didn't get help, but internally they are mostly like "yeah I got outplayed, I lose, let's go next". They mentally minimize the game to be mostly about them as an individual, therefore don't change their style to give their team a chance to carry them when they get behind early. It's MUCH harder for them to swallow the idea of a macro or team focused outplay. They are like, "wtf I was 11-0, picking up a kill every minute and a half, eating their carries, then all a sudden I can't burst the ADC through Janna shield anymore and the ADC who is 1-6 turned around and melted me even though I just killed him 4 times in a row. Janna is broken and this game is stupid". They will ignore the fact that while they were chasing kills across the map, their enemy mid laner acquired a 20 cs lead, they will ignore that despite them killing mid and bot repeatedly, they gave little attention to top side and so their blue buff has been stolen twice so the two junglers are actually quite even in experience, and even though they are ahead 5 tower kills to 3 the enemy adc and Janna were there for all 3 tower kills, and so on and so on with minor things the enemy team has been doing well to stay in the game. They don't understand things like that 1 level is worth nearly 1k gold in stats, so they should have pushed objectives when they first surged ahead instead of chasing kills and wandering in enemy jungle hoping to stumble across someone.
POINT: It's easier for a casual or immature player to swallow a mechanical outplay, but they hate, I meant HATE...losing because they got outdrafted or because the other players are students of the game. A busy parent might give a 3 year old a treat or let them play with their phone to shut them up for a bit, yolo q players are the 3 year old and Riot is the parent and the treat is the snowball win. I agree that things have trended a little too far in that direction, but LOL is primarily casual players so the game will always continue to favor Yolo Q players over students of the game, at least until the influx of new players slows down and LOL becomes viewed more like an Esport and less like a casual video game. I mean think about it, much less toxicity and trolling when you play a pickup game of ball down at the park than in the average LOL match. When we can get the average LOL player to take their solo q games as seriously as someone playing a game of half court down at the park (which is really not all that serious), then maybe Riot can move away from this trend.
