No, Johannes.
I don't have to invalidate your reasoning. You are making the outrageous claims, the burden of proof is on you. This is not an economic or political discussion where we have to rely on philosophical and ideological hand-waving and opinions . We have telescopes for settling problems like this.
We already know the mass of the beast at the galactic nucleus, and we know what it is. We have photographed stars orbiting it at close range, in easily recognizable elliptical orbits and by measuring those orbits Newton' Laws give us its mass directly.
We have video.
The Milky Way contains a super massive black hole which is as massive as ~ 1 million Suns. However we don't see it as being very bright - it is not an Active Galactic Nucleus. The reason for this is that it is currently not accreting anything. Astronomers know that the black hole is there because stars are seen orbiting around an invisible mass very fast, which means that it is very heavy...
...AGNs [Active Galactic Nuclei] are variable on very short timescales which means that they themselves are very small, as the largest size they can be is limited by the time taken for light to cross them.
Your reasoning is irrelevant.