You mean having dungeons where I have to turn my brain on and can't simply pull the entire room while the DPS spam AoE abilities? Yes. I will gladly take increased failure rates over what we have now. Of course, as per usual, you argue in extremes. Progressive difficulty doesn't mean everything becomes unbearable challenging, but simply scales upwards. A direct equivalent would be campaign modes in single player games where you go from Easy to Normal. If such a curve existed, you aren't going to a constant string of disbands because people will actually have to put forth an effort. When nothing challenges, people get complacent. The reason you see so many mess up Tsukiyomi normal is due to how laughably easy the game between the end of Stormblood up to 4.3. Then out of nowhere, you have an abrupt spike that people aren't expecting. That is FFXIV's issue in a nutshell. Constant, random, spikes of difficulty in lieu of a developed curve.
That's precisely what hard means. Why is that such a bad thing? Need I reiterate for probably the thousandth time now The Vault is a good example of difficulty done well. It isn't Rathalos EX level but it's not something you can sleep through. What a novel concept. If anyone finds Swallow's Compass hard, they are either woefully undergeared or haven't bothered to learn how to play the game. Players like this shouldn't be rewarded.
Because the game is piss easy until Shinryu shows up. As I said, when you have sudden difficulty spikes like that, it will create a wall for people who weren't anticipating such a jump. On the other hand, if content grew progressively harder, Shinryu would feel like a natural step. Is it too much to ask casual content actually require two healers?
Even casual players are asking for more. We lost a dungeon because the developers outright admitted people have been finding them boring.
There needs to be a balance. If I recall, WoW swung too hard in the opposite direction which will turn just as many people off as making everything super easy. We've seen that first hand.