agree with all of those. The size of the miter and all kinds of other things involved (as you mention, rail width, all the way down to where the glue hold is strongest in a mortise, sawn orientation of the wood....).
I've learned (in reading about baked wood that's becoming common for guitars now) that over a very long period of time as wood loses its volatiles, it will shrink each time it dries, but spring back less when absorbing moisture, over time shrinking in general. This matches what I see on japanese planes once they're a couple of decades old (and if they're fit tight laterally, tiny movements make a good fit suddenly become an iron that can't be relieved - and their grain orientation is unfavorable for this part of the fit to be favorable elsewhere).
Long story short, this wood is probably starting from a more stable position (KD and already several years old beyond that), but it could shrink over time some more. The miters are relatively short due to the size of the bead and I'm not sure that the furniture will last long enough to see that shrink. (and that's assuming that it would be considered good enough for it to matter - the truth is that the case itself isn't that special and it doesn't really matter -but I still take notes for the next one).
There are other little nits to deal with if you're cutting the bead by hand, etc (the depth of the bead needs to be identical - and I remember from my routering days, even if I was using a router, sometimes the depth of cut varies a little bit) - I'm guessing false cope avoids all of these things and allows for movement, it's just a better technical solution.
For someone like me, who doesn't read a whole lot, and who isn't going to buy furniture-related books, It's interesting that when you go out to google on a topic like this, or mouldings, you get:
* tons of conversations about commercial cabinets and customers (The discussions aren't that technical, more related to fairly blah topics where a customer wants something that they were told by a salesman and a builder does something different) in regard to cope and stick or mitered doors. Joints won't have anything to do with the service life of these cabinets, though - style and color will have them removed and junked or put in a hunting cabin long before construction is an issue
* crown moulding, how to install crown moulding Looking on google a couple of different times on installing furniture moulding on solid cases yielded endless DIY videos and advertising about installing or having crown moulding installed. Totally worthless results.
Thus, asked here.