Grievous was a great general. The droids were quite crappy though. Even with crap droids, Grievous managed to easily wipe out the Nightsisters, the planet of Dathomir making them quite powerful per Sidious. He also managed to beat Maul's Mandalorians in the first battle even though he predicted that the odds were against them.
And Grievous entered the battlefield quite a few times. Meaning he helped his soldiers.