Thanks for all the hard work Evans, so many amazingly good designs over the last years, will be missed.
You nailed it here. It's going to be a combination of what designers want with what engineers can do within cost constraints enforced by others (hello Apple pencil v1 on the new base iPad total cost call there) - and then of course you have the top execs who oversee it all who could affect things.
As others have pointed out, Apple has done astoundingly well under their current CEO, but the company misses someone at the flyover exec level who would put their foot down and say "you know what folks, this really sucks, we can't do it like this.", that Job's did - thinking of Apple Watch v3 carried on for years where you could not do a OS update without doing a factory reset 1st, every single time, or this goofy v1 pencil on the iPad etc..
The company is doing fine without that, but it would do better with someone making these calls and keeping the user experience quality at top notch (for everything). Tough to get someone like that, which the CEO could trust who wouldn't also be an ego centric nut job though.