I honestly don't get this logic. What does the incapability of other characters have to do with Inaho's personality and line of thinking? The other lot are stupid, that doesn't change the fact that Inaho is his own person and a person who can determine things with plans set up by him. Do you think other characters being better undermines/improves Inaho's character? I agree that many other characters are badly developed especially the circumstances they are in. But those characters should be judged by their own ability only, not how they come off as a result of another character. If anything blame the writers for underpowerering other characters in order to get the most out of Inaho.
Him out of the picture will improve things? Oh, please, spare me. Those characters will not function as a proper survivalists even if they were at the death's door.
You answered your own question. Inaho flat-out could not have the presence he has in the story unless he is hyper-competent and everyone is sub-competent. IMO It would have totally been possible to preserve his personality and talents while having a more balanced Earth faction cast with various useful talents, and/or Martian pilots that caught on to his M.O., but neither happened, and neither happened intentionally to make him look better.
And I'm pretty sure I said that removing Inaho wouldn't magically fix anything. But the way he is framed essentially makes him the biggest obstacle to anything interesting being done with the setting or cast. If they won't produce anyone capable of actually challenging someone that competent, they should have him take a hike. Thankfully, they did!
Maybe it is naive to think that they might do something with the void that Inaho leaves in the Earth faction, but what's wrong with hoping that Aldnoah Zero becomes a better show?
EDIT: I forgot I didn't address the characterization part. But unsurprisingly, this is a direct logical extension of the answer to "why is Inaho so excessively competent and everyone else a moron". I think it is honestly difficult to give other cast members meaningful characterization when the intent is to keep the audience's focus on an analytic protagonist who rarely expresses anything and just Gets Things Done(tm). If you went off tropes, those character traits are something you'd expect to find on a supporting cast member instead.
