Honestly I'm still confused how Larian adding origin characters in any way detracts from playing a custom character? Other than the theoretical 'resources could be better spent elsewhere' I just don't get it. Having fleshed out companions (that could also double as a protagonist) in no way overshadows your custom character . . . that argument applies to any companion in any game regardless if they can be origin characters or not. Is it some feeling of loss that you are missing out on content by not playing the origin characters or something? [...]
The problem is not that the companions are fleshed out. The problem is that Origin Characters have backstories and tadpoles whereas Tav only has the tadpole. Thus, the only thing that makes Tav unique and actually feel connected/important to the world ([Baldurian] dialogue tags are not sufficient) is not, in fact, unique.
And the 'theoretical resources could be spent elsewhere' argument is valid. Instead of making Astarion, SH, etc Origin characters, Larian could have added DAO-like background stories for Tav or something similar. Idk how much more work it was to convert Astarion+ from normal companions to Origin companions, but it was probably not zero.