So it's retcon, just like the novel said Maul died in Naboo. Both the Black Sun and the Hutt have no true loyalty to Maul, it's not like they would sacrifice themselves against the Republic or the CIS directly. Even the Mandalorians were mostly deceived by him. Yes he got many men around him, but it is easy to dismiss, the strength is not just about the numbers. Use apprentice to cleanse opposition is what Sith Masters do, and Sidious used it very well. Even Maul could be his apprentice as well if he is good enough to take out both Dooku and Anakin. You can see how afraid he is before Sidious.