Not sure I agree about it being a "fundamental principle" - I mean just look at Gmail app and web mail - used by a billion of people or more so it can't be *all that wrong*...
... although their current "design update" makes me want to poke my eyes out with a rusty spoon
so they're not always right.
It's really a "more streamlined" UI -- hit reply, type your reply and hit Send, done.
But -- there is a setting to turn off the new editor! So even if we end up doing nothing in the new editor about this, or end up doing something which again isn't liked by 100.00% of existing users -- that setting is there and will continue to be for the foreseeable future.