Bottom line, Modern WoW is cool for a short span of time then gets really old, really quick. It's easy to see "Oh well that's 17 years worth of content to enjoy!" Next to none of it is relevant. Literally. If it isn't your faction capital, or 9.0 zones, or the 9.1 and soon 9.2 zone it literally is pointless to be there. World of Warcraft became World of Latest Content Patch very quickly. Then once Shadowlands ends, all the zones in it will cease being relevant and be avoided permanently unless it's some meta leveling strategy to save an hour.
Oh and before I go, classes. This is a fun one. If you're not playing a class or specialization of a class that is in the upper end of performance, good luck seeing parties that aren't matchmade. XIV gives you the liberty to play what you want and be viable to all content, some are better but you can still do it. Not so for WoW. Lord help you also if you accidentally botch a mechanic. You'll see verbal abuse like none other. Liked playing your rogue for years and it's bad one tier? Better reroll. Now what's rerolling like in WoW? In XIV you pop on a new weapon, buy some gear, meld some stuff if you have it leveled. In WoW? ENTIRELY NEW CHARACTER. All those grinds you did to keep your renown in tip top shape? Yeah, you'll do those again on a new character because it's better for a tier and your guild will require it if you want that raid spot.
