As for obligations to continuity--reboots have precious few such obligations. They are more beholden to their own internal continuity (but even that gets sacrificed to the needs of drama--as happens in movies and TV shows all the time).
I agree. Initially I think they considered a pure reboot but rejected it as invalidating everything we'd seen before. This alternate timeline was their way of having their cake (respecting the fans) and eating it too (getting to do whatever they wanted). I think the problem is that if you're talking about a universe that (prior to the timeline divergence) is grounded in the Trek world we've been shown so far, it places some limits on what they can plausibly change. Although plausibility's in the eye of the beholder, I kinda wish they'd just started from scratch. A lot of these arguments would be moot.