Error most MBAs make is thinking we got engine, no work will be needed to customise it. That is why Unreal games feel simply like Unreal games.
I've seen two people start with it isn't that hard. PBR is simple, take Bullet physics, network is fun, cloning Lumen is easy, ... Well, animation is not fun, very few people understand sound, nobody wants to deal with GUI, assimp is in fact limited.
Of course both of them competent people coming from Unreal thinking they are too competent to be limited by Unreal.