League of Legends is largely a team-based game, so when you play in something like b5 then quite often the teammates you get are not very good. So if you deserve to be in s3 or something, but aren't diamond material, you could say that you keep getting bad teams and are stuck in elo hell.
If you deserve to be in diamond and play in bronze 3 then yeah, you should be able to carry your team enough to win.
I guess the point could also be made though that the other team can be just as bad. But if it's a 50/50 chance, for every game you win you also lose one, and it's nearly impossible to advance that way.
I'm willing to debate if you provide a point lol