My opinion is that 5e followed the flaw of 3e where it was designed around the new players, poor players, and other under optimized players.
So once players gained experience and learned the game, they had to form a gentleman's agreement to not meaningfully optimize building or playing unless you were playing a weak PC.
It doesn't take much to learn major single entities were vulnerable to control spells.
It was an agreement to not control down every Boss monster.
I've found it designed more than will enough for most players, not just new or poor players. I've DMd at all levels with few issues. Will fully admit that the published adventures (at least from WoTC) are not difficult for the players. But I've also found that players actually like that, they don't want adventures where survival is on a razor's edge. If you have players that do want that? Yeah, you're going to have to change things a bit. But with experience, 5e can provide that play style.
I think designing specifically to reign in optimizers is a losing proposition. And I'm actually glad that didn't happen. I think if that's the direction the designers had gone, the result would be worse than what we have now.
That, of course, leads to a conundrum. WoTC (the designers there) now has a pretty good idea where the problematic elements are. But 5e is still going gangbusters. Changing things too much could jeopardize that. Just because the product would be better from a "game" perspective (assuming it even would be), in no way, guarantees people would like it more.
Just some thoughts.