Title's a mouthful so I'll elaborate here.
I think the horse's pretty dead at this point and everyone here knows the corner that SE has designed themselves into when it comes to combat content.
Combat is getting stale and IMHO, the fundamental problem is because of the shifting of agency away from the player. Let me just try and list some generic "methods" that a player can engage in combat with enemies in other RPGs:
1. Critical hits
2. Single target damage
3. AOE damage
4. Accuracy
5. Skill/talent trees
6. Element advantage/weakness
7. Damage types (blunt/slash/pierce/maim)
8. Stuns
9. Silences
10. Meaningful Buffs/Debuffs
11. RNG (god forbid)
12. Dot mechanics
13. Aggro management
14. Resource management ala Mana, Stamina(TP)
However for the majority of this game's combat content, there's only.... damage. All your buttons are just different places to press for more damage. GCDs? Damage. oGCDs? More damage. Abilities? Yet even more damage. Everyone is being funneled into a "press all your buttons at the 2m mark" gameplay. How is this fun?
Now we list some done to death mechanics in this game:
1. AOEs
2. Tethers
3. Stacks
4. Spreads
5. Role specific spread/stack
Now what do they all have in common? That's right. Movement. That's all this game's combat boils down to. Deal damage while moving in predefined locations at predefined intervals. And that's the crux of the problem with this game's combat design as of this post. There are only so many ways you can mix the above mechanics until players catch on that they're all the same mechanics mixed in a different way, because there's simply no other way to have interactivity between the players and the boss.
There's now a paradox. There's not much a player can do to interact with the enemies, but there's also nothing new that they can put into fights other than more movement patterns. This is why the combat is getting stale, really quickly. It's all movement movement movement.
Thoughts?
TLDR: Players don't have many ways to interact with fights other than damage, while fights only consist of movement mechanics, therefore combat is quickly getting stale.