I don't think you are off base FWIW. Unity has long both kinda lagged too hard but also just makes things weird at times.
I think the biggest hurdle a unity contender has to overcome, is how to provide both 'similar enough' primitives as well, as a way to easily consistently handle the graphics/sound pipeline (i.e. simple way to handle different platform bindings) while also making sure all of that infrastructure is AOT friendly.
I think the biggest hurdle a unity contender has to overcome, is how to provide both 'similar enough' primitives as well, as a way to easily consistently handle the graphics/sound pipeline (i.e. simple way to handle different platform bindings) while also making sure all of that infrastructure is AOT friendly.