I think you're blowing this out of proportion. Especially when compared to a "fill er up" situation where you'd be even more fucked if you wanted to make your ship longer or shorter. Besides, it's not like power scaling from silhouette needs to be super absolute either, there could be a range of acceptable values or a penalty/bonus system. In the worst case scenario, it's still fewer blocks to add or remove than a "fill er up".
*EDIT* also i've never heard of anyone pre-planning the end mass of the ship, how many years of experience do i need for that level of competence?
I feel like you went on a bit of a tangent here, the topic was balancing power output, not the ship itself. But i definitely agree with you, it's just natural that a smaller ship that somehow could power a larger mass of systems than a larger ship that doesn't make full use of its potential reactor output is going to be more effective even in a "silhouette" scenario.
Are you reading the thread? The point is to have less systems, not none. And if a heavier ship somehow manages to power itself and fights an identical silhouette ship with less mass, obviously the heavier ship has an advantage. This would be true in any system. The ships simply wouldn't be "completely filled", because you wouldn't be able to power that much. That would leave room for crew areas further down the line in development.
I probably made it sound like i was talking about the balance of the entire ship somewhere, sorry about that. English is not my first language etc