It might be unpopular in many players perspectives about balancing around pro play but...
When you think about it, it kind of makes sense. Would you rather they balanced champions around bronze matches where players don't understand how to mechanically use a champion, or balance a champion around pro play, where the champion is being used to it's full potential.
If the champion was balanced around normal play and low level play, then the champion would most likely be looked as if it is underpowered due to the lack of mechanical knowledge, and it would be overbuffed.
If the champion was balanced around pro play where the maximum potential is being utilized of the champions, then it overall creates a more balanced game for all of the players, not just low tier.
The reason being many people complain about this stuff is because the player's using them just don't understand the champions mechanics.