Hihi that was pretty much my friends fear when i told him about RT. hes used to Cthulhu WW1-2 time periods.
When i mentioned the size of Ork Waagghes and the terryfing power of CSM, he quickly understood how insignificant a RT really is.
For epic, i could imagine the RT getting that Crusade started for The Admiral of Passage Watch 27 Est. On top of that, i dont think a RT character willl be good enough to stop (he can try to survive) a Terminator teleport attack on his bridge led by a souped up TT HQ.
Why does this work for RT so well? Because combat prowess is quite separate from the actual "power" level of a character. There is nothing on the advance scheme that represenst a company of Space Marines supporting a small crusade of the RT. Its totally dependent on the RP aspect of the game, but at the same time, nothing on the advance scheme is as powerful as this tool.