I don’t think benchmarks are really needed to explain this. The whole game engine part is an unnecessary step.
To initialize a web browser component within UE5, you first need to initialize UE5 and then the web browser within it. Or, you could initialize a web browser directly, saving the memory and time needed to start up UE5.
They clearly have developers who know how to use CEF or whatever web view framework since they added it to Unreal Engine, so it’s not like they don’t know how to add it to a standalone application.