and where does that interfer with the submesh / surface system?
Internally you will use batching for rendering anyway, something that a model format can never represent ...
As well, nothing actually forces physical materials to be 1:1 tied to visual materials, it actually can but must not.
Having the possibility to have it like that is something I actually would see as a benefit, because if I don't want to use per material I still can assign the same material onto all surfaces on the model and the "engine" can behave intelligent on such a case.
Internally you will use batching for rendering anyway, something that a model format can never represent ...
As well, nothing actually forces physical materials to be 1:1 tied to visual materials, it actually can but must not.
Having the possibility to have it like that is something I actually would see as a benefit, because if I don't want to use per material I still can assign the same material onto all surfaces on the model and the "engine" can behave intelligent on such a case.