Master Crimzon
Baby Killer
Yoda wasn't exactly able to negate the lightning so much as he barely caught it (after it disarmed him, leaving him without his most deadly weapon). And Grievous, while physically stronger than Yoda, doesn't have Yoda's uber-mastery of the force, which could enable him to gain strength and defending ability far beyond Grievous'.
And to MoC, what did Mace ever do that would put him on a level with Sidious? Please. Sidious is the same guy who executed a ritual that clouded the minds of... well, the entirety of Coruscant's population, summoned lightning storms to destroy large parts of its surface. Oh, and he was called a "Black hole in the force" by the RotS novel, and a greater master of the dark side than even Dooku, a guy who could decimate Asajj Ventress by lifting his finger. He also stalemated Yoda, Windu's superior and the 'most devastatingly powerful foe the darkness had ever known' in force abilities (or, depending on your point of view, he might have defeated Yoda). In their very force struggle, despite Windu having the advantages of Vaapad and superior physical conditioning, Sidious was pwning Mace, causing him to 'choke on ozone' and, it was made almost explicitly clear that Sidious would've defeated him if it wasn't for him 'faking' his weakness (supported by GL himself). Do I really need to go on?