I'm not saying it doesn't take years. But a foot is much more easily aligned correctly, the mechanics of the strokes are simpler and there aren't many different things you can do with feet. With hands there are much much more nyances, many different techniques for stroking, buzz rolls, brushes. There's also much more dynamic space with hands than with feet. For example I wouldn't really say there's such thing as half stroke with feet, maybe low and full.
If your only goal is to blast as fast as possible, sure, the speeds of hands and feet might go hand in hand. At least if you only use fingers. But if you want to actually play something else, it becomes much more complicated.
For these reasons I practice hands and feet 3:1. At least for now that ratio gives me about the same amount of progress for both.
I have always wondered how do all these death metal drummers learn their hand technique if they only concentrate on bass drum rolls. It gives all the beginners an illusion that hand technique is lesser and trivial thing while the truth is very different.