I personally don't think it would slow it down enough to improve the game or really even affect how people play much.
Meanwhile, it would mean that there's no longer any punishment for playing basic V support Pokemon, and that's something that I believe would hurt the game.
That said, I'd be fine with it if we get a new Great Catcher but for all rule box Pokemon. I did like the format where we basic only had Custom Catcher and Great Catcher. The best way to slow down the format is to punish Vs and reward/protect single-prize Pokemon. Removing consistent, generic gust doesn't really have an effect. Saying, "it slows it down so it's better" is an oversimplification of the problem with the format.