Maybe a little late for the debate ...
But have any of you concidered that levels are just game mechanic, that have nothing to do with your character? O_o
Well your companions do feel less powerful - most of them Express that along the way, maybe with the exeption of Astarion, who actually feel more powerful ( probably because he can walk in the sun and enter Houses uninvited now).
It cou have to do with the indoctrination process being interrupted for the party members. It's not a great explanation, but one, that might work.
