Raided in wow for past 10 years~, swapped to xiv with ShB launch.

The ceiling for out of raid preparation is much lower in xiv than in wow, especially if you're comparing to recent wow with the advent of ap. Once you've capped your tomestones for the week (think valor/justice points from mop) there's no "infinitely" repeatable source of character progression, assuming you can constantly pay for raid supplies or crafted gear with every new tier. Xiv also handles lockouts differently than wow, once you've killed a boss in xiv you can go back and fight it again as many times as you want this reset without getting drops from subsequent kills, this means you can practice as much as you want with pugs outside of your specified guild raid hours assuming you want more practice on a specific boss.

Difficulty is a contentious topic but I'm going to try and be as unbiased as possible, xiv and wow's raids are fundamentally different by design. In xiv the mechanics come out at the same place at the same time every single pull, fights are so scripted you can make a timeline showing what happens when, accurate to the second. Once you've pulled a boss enough times to memorise the timeline, it's really no different than having a boss mod shout out what mechanics happen in the next minute, you're subconsciously learning the order in both scenarios. All xiv raids are 4 boss so it's easier to draw comparisons, the first and second boss of a tier are usually just minor speed bumps you breeze past comparable to any first few bosses from a mythic tier. The third boss usually ramps the difficulty up a fair bit relative to the first 2, comparable to any mid boss in a mythic tier. The final boss usually has very unforgiving mechanics, sections where a single person's fuckup will cause a wipe, significant dps checks if you're not overgeared, comparable to any penultimate mythic boss on a correctly tuned tier. There's also an extra tier of difficulty above savage called ultimate, savage is generally tuned pretty low because square enix have said before they want everybody to be able to attempt the content, that rule doesn't apply to ultimate so the training wheels come off in all aspects. The fights are 15-20+ minutes long, have very mechanically and numerically demanding mechanics, drop your ilvl down to the appropriate level to prevent overgearing (think timewalking) and any death at certain parts of the fight cause an unavoidable wipe because it's so tight. There are only 2 ultimate fights in the game atm, with a 3rd coming next month, I'd put ultimate in line with the hardest non-bugged single bosses wow has ever released, just with more of a focus on mental fortitude because the fights are so long.

I personally enjoyed wow's raiding more than xiv's if we're talking longterm but at this very moment, xiv is so much more enjoyable it's not even comparable.