Even smaller than the unreal operators is the pool of users that are purists enough to try and keep it all in-box.
Maya, Nuke, Houdini. These are the kings of the vfx world you were looking for if youre talking in the tens of thousands of artists out there, using pipelines that are conceptually 20 years in the making in some parts. The switch from Shake to Nuke was ~15 years ago and theres _still_ nothing good enough to replace it. Foundry scrapes as much money from us as possible because its a good product.
Unreal is amazing. Our shop is wrapping a project using it as the lighting pipeline, delivering to a Nuke team.
Unreal is not the everytool.