Perhaps controversial for me to say.
For most of us in the world looking to solve problems, first you solve it, and if you can solve it that is the hardest part.
If your only job afterwards is to optimize and make it cheaper, that is a great problem to have.
UE in general solves a lot of problems, but ontop of all of that technology they have to solve issues, they also have one of the largest labour forces that knows how to use unreal. That's a major problem that custom engines tend to have, you can't just hire people and they can get right to work, there is a learning period that UE somewhat addresses due to it's popularity in a variety of industries and verticals.
That being said, I think that's one of the largest reasons why MS continues to put more and more of their studios on UE5, one could imagine that they spent a lot of time evaluating between UE5 vs IDTech for the next Halo. I mean, this isn't cheap either, UE has licensing fees that they don't have with IDTech which they own.
One must imagine, that they don't fear the optimization challenges that this thread continues to harp on - as much as they fear not being able to get content out in time, and I very much think that's understandable.
They will have 3 major studios (NT, Halo Studios, and Coalition) all working Unreal, their extensive knowledge of the engine runs deep. I think it would be fair to say, if they can't get performance to work, then perhaps no one other than Epic can. But MS has a pretty good track record here with UE.