I personally don't think this has to do with the JP people being inherently better but that people in rank C and B are a lot more common than people with A and S ranks. I'd guess that the matchmaking system first tries to find people closest to you ASAP, and if it can't get them it'll move on to JP players.Honestly at the higher ranks I'd say regional match making would significantly increase the match making time for higher ranked players. I genuinely think that there are just a much higher amount of Japanese players at A+/S than American players. On my alt account I barely see Japanese players in the C's and B's, even though I'd play at a time when I'd normally get Asians on my main acc. It's more of an average skill problem than a match making problem in terms of all the Japanese players you get in lobbies.
But yes we do need regional matchmaking....