Every MMO ever tried to copy WoW for quite a long time. Why? Because it was the top MMORPG and given how rare it is for a competitor to succeed, the best way to convince any investor is to assure them it will copy its best competition.

But to an extent you're also wrong. FFXIV has many things that are different as well. There are games that copied WoW a lot more precisely than FFXIV, such as SWTOR, which was an actual carbon copy of WoW with lightsabers. They've since begun to copy lots of things from FFXIV for the same reason (I noticed they just did their graphics update to much the same mixed reactions as here).

They did initially try to ignore WoW and just copy FF11. The result of that was 1.0 which was a commercial failure. So at that point what other option was there than to look at what the top MMO was doing?

I do agree that they could take inspiration from some aspects of the single player games better to create other experiences though:
  • Narratives that involve internal conflict between main characters.
  • Being able to use items on eachother. Just for fun, but also useful for people that didn't unlock other jobs.
  • Take the hunts right from FF16 and replace our current B ranks with them. It's a night and day difference.
Maybe use the various battle systems from those games to inspire other mechanics too, such as:
  • The power configuration in FF16.
  • The materia system from the original FF7.
  • The slow but more strategic battle concept in the older games where the long recast times forced you to decide whether to heal or attack. To elaborate on this, it's easy to go on a healer and spam your DPS button 100% of the time, but if your recast time was 10 or 20 seconds, you'd have to consider more carefully whether your next action is an attack or heal because you won't get another chance for ages. The rest of that time could be spent doing mechanics. The game was at least closer to this before they added all these ability heals which completely evaporate that choice most of the time.