I can understand why someone might want to have two accounts to maintain a "high water mark" and continue to play without risking it. I just don't understand how that is a problem for the rest of the user base. Basically, if
everyone ran two accounts and did this I don't think it would lead to a degenerate arena state, and for me it wouldn't make any difference to the quality of the games I am joining. Arguably someone playing on a 2nd account promotes a healthier arena than if they reach a high rank and stop playing entirely, because there is still an active high ranked account for other players to play against and beat for points.
As for a player running 100 accounts, if someone has the time and energy to do that more power to them. If everyone playing a given game was running 10 or 20 or 100 accounts that would lead to a very active arena system (after all, they need to play a LOT to get all those account's ranks up) and a much easier time finding an appropriate match.
I will admit that despite the fact that I play the majority of my games in arena, I don't actually care about climbing the ranks or where my position is at the end of the season. From the perspective of someone who just wants to play with a competitive mindset, someone having two accounts that never interact with each other doesn't impact my experience at all.