You can't fix boosting, because it is the way ppl make money, so there is much more of the interest behind it than around (your personal gaming experience). That is one reason nobody will actually track account sharing. And the other reason is that it is very common even for non-boosting purposes. So the rule of account sharing basically doesn't work at all.
If you have problems with the smurfs, then this is just your individual skill issue. L2p and you can smurf diff them or play at the rank where nobody can smurf (immortal-radiant) - and that is the point of any competitive game. Otherwise, you just waste your time and got punished for not improving as a player.