[@PrinceAlexus]Yes, but no...

Yes the mechanicum hold a high seat of power, but if it came to a fight, the regular Imperium would win. The lore friendly horus herecy series goes into detail about this. When the Emperor came, he was going to demand their respect or conquer them, but they thought him the omnisah, which gave him a hold on them. As time passed however, the mechanicum felt lied to, and to an extent, they were. They didn't have the power to attack them, and cutting of supplies would only come back in turn with violence. This eventually led to horus using this to make the dark mechanicum, but they were defeated by their own greed. In the 4th millennium, the mechanicum work as equals, but still, metaphorically, have a gun to their head. Yes, they have power, but people still see them as simple tools to be used. Very few in the imperium see them as people, if anything they see them more like xenos then anything. Those that do see them as people have spent time on forge worlds or mars itself. Tech marines are good examples, but they have split loyalties and if the two were to have a war, they would be unreliable to the mechanicum, and the imperium would see them as untruthful. So, the mechanicum are still technically the imperiums b!$#%.