Its ffxiv combat really so slow and boring?

[Penthea]

Yes, combat is boring. But not because it's slow. It's only interesting when there are lots of mechanics happening that you're unfamiliar with, because once you're familiar with them there's little if any variance and you fall into a routine.

Which is also why low-end content*, FATEs, hunt targets and Diadem/Eureka (effectively hunts/FATEs) turn some people off. The minute you remove the "dance" aspect of the game you're left with only the job's rotation. It's nearly as engaging as hitting a striking dummy.

* Low level content has little in the way of oGCDs, which speed up the pace of button pressing, and depending on fight also have less involved/obsoleted mechanics.

Even faster paced games can have boring combat if there is little to do other than just spam your rotation. No matter how mechanically interesting a class is, it eventually becomes dull if the encounter itself is little more than a target dummy.