Crowd bonus? What crowd bonus? That wouldn't aid Shaak, that'd make it that much harder to defend against... And I'm referring to the portion of the fight before she got the staff. Hence why there's no context for me to add here. She, with her lightsaber, after just running around Coruscant, fought a large group of them, for a minute, before getting disarmed. Seems comparable to Kenobi having pause with one MagnaGuard superior to the ones Shaak fought and using the Force when he couldn't defeat three.
The Magnaguard Obi-Wan fought is either the same or weaker than those the she fought, as it's said Grievous hand picked the best to kidnap Palpatine...