I wouldn't call WoW the first that defined it, or even the first wildly successful one that did. I never played any of them, but EverQuest was huge back in the day. If we are willing to lower the bar of success, there's predecessors to EverQuest as well.

Then again, maybe there's something very different than WoW and EverQuest that I'm not aware of? They seemed pretty similar from the outside.

The concept of 'shards' which many MMO games embraced (sometimes not even supporting as many players). Only Eve Online really rejected the idea.

The in-game 'economy', by having player craftable items, done in a way that IMHO was way better than what WoW came up with. It wasn't restricted to crafting. Mages could charge for portals, ditto for healers. There was robbery - you could either demand money or pickpocket people.

Law enforcement was limited to cities and had to be called.

Housing! That was actually in world, not another instance. There was actually a real state market. And scouting for empty spots was a viable 'profession', even if informal.

Full PVP - in fact, I'd say that the non-PVP servers actually caused its demise.

One concept that was not embraced by later MMO games was 'no levels'. Only had skills and attributes. And items were not a big deal. Sure, you could yield a very rare magical sword, but are you really going to risk losing it? Most people would fight with cheap weapons and armor and only take out the special stuff in limited circumstances.

I could go on.

I think there's a modern 'Ultima' game that could be birthed from what Origin came up with decades ago.