I sort of like all the TOS villains as they stand, sit or tapdance.
Certainly Rua'fo doesn't deserve to be sympathetic. The very idea is that Starfleet has mistaken him for a mere sleazebag when in fact he's Mengele disguising as a sleazebag. But I agree that his sympathetic sidekick could have been given a tad more airtime; it's just that too much exposure would ruin the final surprise in which we learn how villainous Rua'fo really is - the fact that they are relatives of the Ba'ku. The whole movie is about being in the dark about facts and making hasty decisions; exposure would backfire by default.
Timo Saloniemi
The problem is, the plot twist in Insurrection was stupid and made no sense, so sacrificing potentially compelling villains for the sake of a dumb plot twist. This plot twist brings up a million questions that never get answered: how the Ba'ku force the Son'a off the planet if they are pacifists, after being defeated by the Ba'ku? Why didn't the Son'a just create their own city on the planet? Why didn't the Son'a just go the Federation and lay claim to the planet considering the Prime Directive would theoretically let the Son'a practically do what they want with the planet, etc?
In the problem with the villains is part of the bigger problem with the film, Insurrection doesn't know if it is silly light hearted film or a serious film with a heart wrenching moral dilemma. If it is just supposed to be light hearted film, Rua'fo should have a just a pure evil invader who had no justified claim to the planet (as it stands now, in the film the Son'a had as much as a valid claim to the planet as the Ba'ku did) and simply wanted to become immortal. He would be just a clear evil that needs defeating.
If this film was supposed to be a real moral dilemma, Rua'fo should have been made into a more sympathetic character and his claim to the planet should have been addressed in more detail or failing that they should have ditched Rua'fo and made the admiral the main villain, both the admiral and the Ba'ku both having valid points that are both given weight. As it stands now, Rua'fo is the main villain and he is one dimensional cartoon villain who is made unintentionally sympathetic due to a last minute plot twist, its the worst of both worlds.
Also I think Kruge is a decent villain, but I wouldn't put him up there among the best cinematic villains ever. We know his immediate motives, but we really know his deeper motives? Is he a justified Klingon patriot who seeks to protect his weapon from a potential Federation super weapon or is he some sinister social climber who merely wishes to improve position within the empire and thinks stealing Genesis is the best way to do it? Does he merely want to destroy Genesis to protect his people or does he want to use Genesis for his own purposes and use it against planets that could defy him? In my opinion, he is a decent villain, but not quite a great one.