The gameplay changes from 2-3 and 3-4 isn't why the roster changed the way it did. The roster naturally changed because it was time.
In this game's case, we're getting 30 returning characters from Tekken's history. You can be upset about no Lei, Michelle and Anna but that isn't enough to completely hurt this game's roster compared to the 30 returning characters. It's not really comparable. That's just a few long time fan characters missing and regardless how much they're loved that's not enough to put a major dent on the roster. You're just attached to these classics, which isn't bad, but still you can't really say this is abnormal when they've done far worse with previous games in the series. T3 and T4 stick out way worse than this title especially T3.