Sorry for the shitty sarcastic tone. Usually toss it out when people are saying things like "get good". If you actually want a discussion I'll be glad to do it.
First off, you'd have to separate the concepts of difficulty from design. Bismark Ex was an easy primal for sure, but that doesn't make bismarck an unintuitive primal. He was pretty straightforward and didn't require the player to do really weird things like feeding golems meteors. We can take Mario for example. Mario had pretty straightforward mechanics. Don't get hit by goombas and don't fall into holes. It's simple right? Yet Mario also has a level 1 and a level 6 or 7 or whatever. The difficulty in it wasn't from there being a bunch of new things every level. The difficulty from Mario really just came because things moved faster and the margin for error was smaller. All of a sudden the jumps were harder to make or the timings on it were a bit tougher. Anyone can figure out that fire = pain.
Right now, I find that dodging AoEs and keeping up DPS is a pretty good way to be difficult while also not being convoluted. It's not exactly hard to dodge an AoE. And it's not really too hard to DPS. But it's harder to do both at the same time. The game throws the difficulty at you but it's not difficulty from a game knowledge point of view.... It's difficult because you have to do two things at once.
So while I enjoy taking down difficult content... I don't enjoy putting in countless hours memorizing the completely unintuitive. I enjoyed fights like T11 where it wasn't super mechanically complex but you had to learn how to execute. First there was nerve gas... Simple enough. Then came missiles which also wasn't too bad though I wish stack/split was a bit more obvious. And then you had tethers. It was 3 mechanics for the entire fight. But the difficulty of dealing with tethers and missiles at the same time was a bit harder than each of them by themselves. And if Square had wanted to make it harder they could have shot more missiles and closer together. So all of a sudden you and the person you're tethered to have to dodge 5 or 6 missiles in a row all while maintaining your tether. Or they could have shot a constant stream of missiles and nerve clouds.
I mean sure, people might clear content faster.... But if the lifetime of your content relies on being obscure and unintuitive it's not really good content.... See T5 twisters aka "how the fuck did I randomly die".
Other examples of difficulty while being intuitive is positioning in LoL/Dota, skillshot accuracy, cooldown management.
Or what about mobility/positioning. Most bosses in XIV kinda just stay in one place which is kind of stupid. If bosses were constantly moving, ranged players would have to constantly be kiting and updating their position. If bosses were constantly moving around and then Square lowered the CD of mobility skills to like 15 to 20 seconds perhaps this game would be a bit better. I'm thinking about this in a LoL/Dota sort of way btw where you want to be constantly updating your position to the most favourable. Of course Square would need to lower their positional update from 0.5 seconds but then again... They should be doing that anyways.
See the thing that I found weird about FFXIV is that it's probably the only game I can think of where there was a mountain of mechanical knowledge required to clear it. Most games use the same mechanics but make it faster or give less room for error. When you got to level 2 of Mario, Bowser didn't suddenly pull out a pong paddle and force you to play a completely different game did he? He just made you have to dodge better and be more precise with your jumps. So how come Nael Deus Darnus decides that after playing Asteroid with you, he wants to play DDR? Almost every single game I've ever played has relied on teaching the player what to do and then cranking the difficulty up once the player got the hang of it. It was never play one game then throw everything out the window in phase 2.