The problem with balancing in this game is that there isn't really a good answer.
If you balance for high elo, (which is typically what I suggest) because it's a team game certain picks just become pubstompers. (imagine if yi or Annie was viable at a Challenger level for more then just one tricks, what that would do to low elo)
And so some consideration must be granted in part to low elo. However also considering the dynamic of a team game, unique interactions have to be balanced around also. If, for example, xeyah and rakan had a 90% winrate together you have to nerf that combination.
Now the team game aspect effects this a little too. As people have to work together to win, which makes it feel really bad if a pubstompers that you personally can deal with, gets fed off of your teammates and carries the game.
All that being said, I would rather that riot did a little more catering to high elo because everyone below diamond can technically just get better at the game to overcome any percieved inbalances that they face. (considering that the lower in elo you go the less balance actually effects anything anyway)