Unity is still a lot more popular then Unreal and alternatives exist and are created all the time-- others have mentioned Godot, or Cry Engine which are old. People are working on Rust engines. Lots of commercial developers use their own tech. Game engines don't have to gravitate toward a standard. They only do when the cost/benefit works in their favor.
No it's not - I know a few people who work in the industry and Unity's dead on new projects - everyones moving to Unreal. Indies, etc. might still use it (or other engines), but professionals have been constantly moving away from the engine for years, for all sorts of reasons, the recent licencing shakeups being one of them.
It seems this is getting downvotes, so I need to clarify that this doesn't represent any sort of personal bias - it's just that Unreal has way more (and better paid) jobs than Unity does.
Unity took all the buckets outside, burned them, then demanded money from all their customers. I've not seen new projects using them, because stakeholders are concerned about surprise expenses down the line.
Which AAA games are Unity? Maybe my understanding of the term is more subjective than it actually is, but Wikipedia's chosen examples - Pokémon Go, Monument Valley, Call of Duty: Mobile, Beat Saber and Cuphead - are either very badly downplaying its use or showing that AAA means something very different than I think.
I don't think there is an "official" definition for AAA, since it's mostly a buzzword. However, according to Wikipedia AAA refers to games "distributed by a mid-sized or major publisher". In that sense, I think all of the games you listed fit under AAA.
I personally would consider AAA to be indicative of the game's overall budget, but without looking up the develo
