I assume you mean a weaker form of Grundy, like the one that appeared in Batman Long Halloween or a recent issue of Green Arrow.
WAYLL....
Grundy is indeed stronger. But Bane shouldn't be counted out--he's a skilled fighter. Afterall, Ra's Al Ghoul considered him worthy to be the Ubu (#1 Henchman).
I think that in a featureless environment, Grundy would overpower Bane. But give Bane some way to use his mind, and he could triumph.