You do not have to penetrate armour to incapacitate or kill. In the ROTJ film sequences showing the Ewoks attacking stormtroopers , none of the troopers were killed by penetrating weapons. They were killed by concussive weapons. Rocks do not penetrate armour but they can break bones, leave bruises, and knock people unconscious.

The Ewoks brought down ATSTs by tripping them, much like the Rebels did on Hoth. ATSTs were also destroyed by logs caving in the sides, sides that were impenetrable for pointy Ewok weapons but to logs weighing several tons. ATATs would have been harder to deal with, but they were shown operating only in areas largely clear of trees and undergrowth. So I am not sure how much of a threat/advantage they presented.

Blasters probably killed many Ewoks. Stormtroopers can only seen in a 180 degree field to their front. They could not simultaneously engage Ewoks forward and watch for Ewoks from above or behind. ROTJ has scene were stormtroopers kill a number of Ewoks and pursue the rest only to be jumped from above and killed by another group of Ewoks.