What is ELO Hell?
This post is long, but illuminating, I think.
People point out that if you are playing below your 'true' elo then you will climb. And that's true.
ELO hell is when it takes way too long.
Let's write down a simple model.
Suppose the team with the most points wins, and a team gets a point by 'winning' a position. If your team wins top lane, loses jungle, wins adc, wins support, and loses mid, then your team gets 3 points, the other team gets 2, and your team wins.
Suppose you always win your lane. And the other lanes are determined by a 50/50 coin flip.
Then you lose if and only if three or four of the other lanes lose. That's a a 5/16 probability. So you have an 11/16 or 68% probability of winning. Pretty good. You'll climb elo quite fast that way.
But now let's say the lanes are not weighted equally.
Mid lane is worth 3 points and the other lanes are worth 1 point. So the only way to overcome a mid lane victory is if all the other lanes go the other way. That is, mid lane is three times as important as any other lane.
Now, suppose you are top lane and you win top lane every time. If your mid lane wins you are guaranteed to win (and there is a 50% chance your mid lane wins). If your mid lane loses (50% chance), then your only chance of winning is if jungler, support, and adc also win. There's a 1/8 probability of that occurring. So your probability of winning is 0.5 + 0.5 * (1/8), or 9/16. That is 56% chance of winning. While you'll still climb, it will take a lot longer. Moreover, it assumes you win your lane EVERY time. If instead you win your lane only 70% of the time, your odds of winning the game drop to about 53 percent. Not good. It will take a long time to climb elo at that rate.
Not all roles and not all champions are weighted equally. Assassins, especially back when they snowballed super hard in previous seasons, are like the mid lane example above. They have a huge amount of agency and they take it away from other players. If you were playing a tank top back in those seasons, you had little agency. Even if you won lane the vast majority of the game, it wouldn't be enough to make up for the other team's mid lane assassin who snowballed out of controlled and used it to destroy bot by roaming more often than your tp was up.
This is ELO hell -- when you play champions or roles that are not as impactful and consequently climb slowly even when you play your role well.
Now suppose you are the mid lane assassin but you aren't that much better than average. You win lane 60% of the time.
Now you win the game with probability 0.6*(1-1/8) + 0.4*1/8 = 57.5% probability. That means you win games more often by winning mid lane 60% of the time than if you played and won top lane every game. (!) It's better doing only a bit better than average in a role that is very important than it is to do extremely well in a role that is not as important.
Of course the model is simplified. Your contribution to the team is not just winning the lane; you can win the lane to different degrees; and which lanes or champions are most impactful shifts with the meta. But the lesson still applies:
(1) feast-or-famine champs are bad for the game because they take away agency for all the other players on the team.
(2) ELO hell is real and it is when your teammates play champions with more agency or lanes of more importance than your champions or lane. If you truly are better than your ELO then you want to play the high agency champions and play the most important positions in the given meta.
**Summary: ELO hell is when you climb elo slowly because you play champions or roles that have low agency. Feast-or-famine champions have high agency and are bad for the game because they substantially reduce the agency of all other champions. If you are better than your elo and you want to climb elo, then you should play feast-or-famine champions because they have more agency. **