Not sure if it's Yamaha's keys that are too shallow or your regular piano's keys that are too deep (what piano do you use to play, and which Yamaha model are you comparing it too?). But key depth can be modified somewhat by regulation.
As far as model numbers go, I think most people would agree that the C3 is a big step up from the C1 and C2. I have heard some claim that the Japanese assembled ones are better than the US assembled ones, and those in turn are better than the Indonesian assembled ones. But that's just hearsay to me - I never bothered to check which country assembled the Yamahas I played. And, relating to your key-depth concern, I haven't personally come across a Yamaha whose keys I consider too shallow (well, may be except a couple of really dinky uprights in my childhood).