I suppose I might be in the opposite myself, as the Oberth hull seems to be one of the few that looks specifically modular and also cheap to produce. I can easily see where it would have led to a number of different variants that could perform specific missions.
Unfortunately, we never actually saw any such modularity whenever we saw an Oberth on screen
We didn't with the Nebula after they got the triangular section as well.
Probably just too expensive to build a new module of the same quality as the rest of the model every time it appears.
Thank heavens for suspension of disbelief, eh?