Well, that's where our opinions differ. I don't believe at all that Rossiu is out to usurp all the power for his own personal gain. He's just incredibly cold and efficient about things: The people want Simon dead? He's gone. I wouldn't be surprised if he killed himself if he thought it would be the best course of action.
Of course, it's not exactly a completely sound decision, but we have two completely different extremes clashing here. One of complete and careful restraint and one of unyielding force and bravado. Rossiu wants things done efficiently and with very little risk. What if Simon's survival were to get out? The people are already pissed off about becoming possible casualties due to the actions of the former Team Dai-Gurren. Imagine how they would react if they found out they were being lied to? Lord Genome's head could be easily disposed of, and unlike Simon there's not much chance for the secret getting out.
Rossiu is arrogant, so he believes that he's the only one of his former comrades that can properly run things. He's probably right, since the only reason he has so much power in the first place is because everyone else has no idea how to run a government. I really doubt he initially wanted to shoulder all the responsibility, but he probably realized that the people around him had no idea what they were doing. Thus, while they may have kept their positions in the government, they merely became titles as Rossiu slowly took on more and more of the job.
They're all from underground villages, but Rossiu is the only one with any sense of how to run things. Everyone else is too hotheaded, violent, and impulsive. Say what you will about his current methoRAB, but he had to have been doing something right for the past seven years for things to have been so prosperous. If he would just stop thinking like a machine, I'd say I'd rather live under a government under Rossiu than say, those slow-witted twins or Kittan. And Simon... he's a nice guy, but not the kind of person you want running a city.
Rossiu brought Lord Genome back because it was the only way to find out everything behind what's going on. I believe that he shouldn't have been so secretive, but Rossiu is one of those people who believes that the 'enRAB justify the means'. He's cold-heartedly efficient, as his comments on Kamina's death being good because it gave the group strength, but not evil. If you take all the sentiment out of things, he has a point. Not the best way to think, and I certainly don't agree with it, but he's hardly the monster people are making him out to be. He's a good person at heart making some very bad and unemotional choices.
If he was truly out for personal gain, he would have never swallowed his pride and relinquished the core drill to Kittan. What would be the point? His worRAB as he does so sum it all up "I used to believe in this." In other worRAB, he threw away the dangerous, reckless, erratic ways of his comrades and instead turned to "safe", planned out, calculated logic.
