Noctem
Explorer
I think the key here is: 5e is not trying to offer a completely consistent and fully-defined set of rules. There's no reference in the usual damage process to "excess" damage, only to "remaining" damage, but the polymorph rules talk about "excess" damage. But that's because you are assumed to be able to figure it out.
And that's honestly a better design most of the time for most players. But it does mean that there is simply nothing in the game rules as written that fully defines/resolves some ambiguities.
Which is both a blessing and a curse imo because of how much time and resources they are now having to spend explaining all of these things that should have just been (imo) explained in the first place ESPECIALLY if you're going to have Adventure League for example. You should never go from one DM to another in AL and have different rules. This is something that's actually specifically stated in AL guidelines, and yet, that happens quite often. So what causes that? The ambiguities which are the product of deliberate design choice. So in conclusion it's nice to see that some people think this gives them more creative freedom but imo there's no barrier to creative freedom with having a solid rules base for everyone to use and the modify as they see fit. You're only limited by your own imagination and willpower.