One of the things that stuck out at me was the lack of "superior ambition" among Khan's people. They have a super-weapon, a WMD, now. Joachim calls him down on chasing Kirk, but why didn't he try to take Khan out and become the leader?
Khan had the ability to inspire actual loyalty in his people, as we see also in "Space Seed." Presumably because they believed as he did that he was the best of them (his having successfully kept them alive after the unexpected cataclysm on Ceti Alpha V would have reinforced that aura of superiority). That Joachim wanted to restore him to rationality didn't mean his loyalty had lessened.
Also note that even through his mania Khan retains a parallel fixation on Genesis once he's learned of its existence? He would have learned from Chekov and Tyrell that it was more than a "superweapon," it could also provide his people with a new planet. I always took this to mean that even at his maddest, some part of him was still thinking like a prince. It was not so hard to see why his people remained loyal.
(Incidentally, it's instructive to watch TWOK having read Moby Dick
. The Trek film is nowhere near Melville's league artistically, but it makes it easier to see what kind of character they were aiming for in their version of Khan once you know the original Ahab. Also Moby Dick
is just a really good adventure novel.)