Latecomer
The reason Sombra doesn't always use his mind control (besides it being a later invention) is because those without minds of their own can't feel fear or despair. He wants this for both practical purposes (to spread such feelings to neighbouring lands via the Heart) and because, well, he just enjoys weeping slaves who hate him but don't dare defy him more than ponies who are basically fast asleep. So at most he used his powers to create loyal guards and overseers (since he seems to have lacked any true supporters) while the rest of the populace was kept in chains and tormented.