I keep seeing these posts about how Grievous is nothing without Sidious and Dooku, and I have to say that that is only partially true.
Sidious had Dooku get Grievous because he wanted a capable commander for his impressive droid armies. Sidious was not whispering in Grievous' ear and telling him what to do. The war effort was Grievous (and the other military commanders). Dooku served as the political icon for the Seperatist Alliance, and did not even bother with commanding troops. We read in Dark Rendezvous that Dooku doesn't want to command troops.
As for the loss of the Seperatist Alliance. Grievous could always use the Tarkin Doctrine to keep them in line, and we know that they are all cowards so that will work.
Here's the thing: it's not that Greivous isn't a great commander without Dooku and Sidious telling him what to do. I believe that Greivous often made his own successful plans. But we were rating Greivous earlier based off of his war with the Republic. Sidious was often pulling the strings to expose/weaken the Republic. Imagine how well Greivous would have done in the war without Sidious. He wouldn't have been quite as successful. That's the main point here I think.