Of all the firing decisions at Xbox this is the most shortsighted. Do you think or how has competing with the world on another UE work for you? games would run worse , feel worse.
You should be encouraging more people to use Idtech.
IIRC Doom Dark Age sold 3m? copies, so it would cost $10m in Unreal Engine fees. Doom Engine team likely cost more.
Microsoft problem is it is giving away games for free on gamepass, so it sees its engineers as cost center.