That I can agree on. In terms of numbers, Grievous does have the advantage. He probably has 6-1 odds on Malgus. Yet as we know, for all the Numbers that Grievous had, Jedi and the Clones have been more than matching them to the point of a near stalemate. The difference here, I'd say, is that Malgus' forces are more varied, with different species and ways of fighting, along with Sith War Droids. Plus Malgus has the Schism Collective, a group of alien scientists dedicated to advancing the weapons and technology under Malgus' command. One such being the Flux Cannon on Malgus' space station, which can completely destroy a Capital Ship in one shot.
I thought the rule was that all tech was the same in this debate because:
Any tech made by Malgus and his scientists would alreay have been invented by Grievous's era. If you want to argue that Malgus has better tech you will lose, because anything he creates the CIS will have / know about.
The "more ways of fighting" argument is completely not true. The types of droids used by the CIS were numberous, and let's not forget that there was more to the Confederacy than droids.
Click this link and scroll down the page to "Members" for a full list. http://starwars.wikia.com/wiki/Separatist_Droid_Army
The innovation and unorthodox tactics used by this large number of different droid types and organic soldiers puts Grievous at an advantage for the "more ways of fighting" arguement.