smurfs

Technically boosting in a moba on a moba in solo queue happens in 2 ways. You play yourself en let your diamond (or whatever high rank player) friend make a smurf. Put yourself in a "worthless" role so you don't have to have a huge impact both winning or losing (aka feeding) lane.
Let your high elo friend stomp his lane because of the huge difference and carry the game on his own.

The other one involves pretty much giving away your account to a high lvl player.

The top 1 is not that bad true. Unless we're speaking a bronze player getting boosted by a plat player.
If it's a plat 5 boosting a S1 the difference is way less of a problem. And the boosting will become a lot harder.

Biggest problem you will have yourself is falling down quickly when you solo queue. Making any other unfortunate soles on your teams games ruined

At some point at higher elo, the "bronze" teammate won't be getting carried easily.

Unless we're speaking a bronze player getting boosted by a plat player.
If it's a plat 5 boosting a S1 the difference is way less of a problem. And the boosting will become a lot harder.