Keldor would have been a good king, you can’t change my mind.
As Keldor is leaving Eternos (because he’s been banished for a crime there is no proof he committed), yes, his main thoughts are of the crown that was taken from him, but pay attention to what he actually says:
“...I will unite my people! One language, one race, one planet. I will rule my Eternia!”
Unlike Miro, the King before him, and unlike the vast majority of the citizens of Eternos, Keldor dose not see all the different species of Eternia as different races. Human, Beastmen, Gar, Aquaticans, etc. they’re all “Eternian” to him. One people.
I think that is a good view for a leader to have.
And, he maintains this view even after he’s become Skeletor.
“Protect the people, all of our people. Human and Gar alike. You must swear this.”
As Skeletor lay dying, having finally been defeated by King He-Man, his last words are not vows of vengeance, or a curse upon his enemy. No. His last words are a plea that Adam, as the new King, will serve all the people of Eternia, regardless of it they’re human or not.