I love how a single UA, not even official material, makes people think that this is the new normal. There's no guarantee that the classes in the Strixhaven book will even make it into that book, let alone in the form that they are showing. And, there's no guarantee that any subsequent books will use these mechanics. They might or they might not.
Note, this is different from the lineage changes since that wasn't a mechanics change per se, but, a reaction to other issues outside of the rules of the game.
People tend to forget things like the fact that we've had, what, three different stabs at psionics without a single psionics class becoming official. The UA ranger has never made it into print. Heck, a large swath of stuff in UA doesn't make it into print.
But, yeah, "subclasses are no longer for one class" because of a setting specific book that hasn't even been released yet.