Obviously, there are no true Scotsmen. But whatever you think of it, unity is widely used by indies, especially in mobile and VR.

So given that, would they consider Unreal to be a AAA game engine?

Generally it's judged by the types of games which have been produced. Since Unreal has had AAA games released using it, then yes I'd say so.

So then having a GC isn't an impediment to be a AAA games engine it seems.

I didn't mean to imply that it was. But it's not ideal. I believe it's optional in Unreal too, so I'm not sure if AAA games use that feature.

GC is also a very blanket term. There are many different types. From what I understand the Unreal GC gives you a lot more explicit control over how and when it runs.

Having written OpenGL applications in Haskell (not games) I can say that it has no such feature. It's GC is also vastly different as immutable functional languages generate a LOT more garbage than normal applications (measured in GB/s).

GC is not the impediment. GC as it is currently implemented in the majority (if not all) advanced type system functional languages is.

There I agree with you.

However Unity is improving their performance, you should have a look at HPC# presented at GDC 2018.