I thought Unity and Unreal were transiting to ECS? I was under the impression at least that Bevy was adopting what the industry was moving towards, not exploring virgin territory.
I'd very much consider ECS virgin territory. DOTS (ECS) in Unity has been out for 5+ years with little to no real adoption. I'm unaware of any pretty much any use of ECS in Unreal (I think what exists is mostly focused on internal graphics / animation, not gameplay).