Believe me, I really don’t care to defend Bethesda. I’m not saying their engine is incredibly good.
I’m mostly saying, I feel like their games would be different and even more AAA-generic, if they built it on top of Unreal or Unity. And I’m giving them mild props for not just buying into the duopoly.

But I’m also just saying that, as a result of building their own engine, Bethesda can’t just quickly prototype something. To see what the final game looks/feels like, they have to invest years into engine development.