So many baseless assumptions.
How will people not be happy about it? Have you asked all of them?
Also yes a lot of raiders are capable of clearing all Savages at min ilvl without looking at guides because they are genuinely not that hard and at this point people have already seen those mechanics used over and over again so much it's hardly blind.
I think that makes sense but everyone is at a different stage of learning the game. Stormblood worked fine because outside of Ultimate, the difficulty gap was more narrow. Endwalker's difficulty gap is at the game's most extreme (for combat content) since its inception. On the one hand you have what is pretty much a visual novel. A very good one, but still a visual novel experience. On the other you have what is probably one of the hardest raid mechanically across all MMOs, period. This gap is too insane and like you said comes from trying to cater to people of all types.
But I think at this point the players themselves have a wide divide between them. While it would be nice in theory to strike a good balance, I think there needs to be at least one more difficulty level. Otherwise you'd have to narrow the gap to strike that balance. I am personally against narrowing the gap if it means lowering the difficulty of Ultimates. But I can also understand why some players wouldn't want to narrow the gap by increasing the difficulty of the MSQ.
Striking the balance would be great for midcore content like alliance raids, Bozja, EX and even Savage. But it doesn't really bridge the gap between the two extremes IMO: what you'll have left would be a big, packed island in the middle of an ocean (the midcore content) with MSQ lying all the way to the west by itself and Ultimate an entire ocean away.
The gap has to be filled somehow and adjusting the extremes would be something I'm against. But there isn't enough difficulty levels in the game so that they can fill in the gap without having a spike somewhere.
What you're suggesting could work if there was enough creativity and genius for them to design content that can bridge the gap while being repeatable so you can keep training to get better. For example, a Bozja duel that keeps getting harder and harder with more mechanics thrown at you over time, so that it acts like a difficulty slider in one single piece of encounter. But for the most part no such content exists in the game currently.