Note -- This is an older observation from when GoD first came out and I made my berz...things could have changed.
Skill ups in frenzy seem to do 2 things : Allows frenzy to connect more often, and gives a greater chance to have more than 1 attack.
Of course, I could be wrong, and your weapon skill may be tied to whether frenzy connects or not.
Anyway, that's the gist of it. Frenzy does NOT use the damage associated with your current weapon (or if it DOES, it's very, very minimal). Instead, it seemed to be a basically set value, which sorta sucks.
Of course, this prevents people from making a quick weapon switch when frezy pops, just to get the damage from a powerful but slow weapon, then switching back to a better weapon.
What I tried: Using a two-tined corpse pitchfork, I would swap weapons to a weighted axe. It's crap, but it's high damage.
THe frenzy damage remained the same, though, even though the axe had almost 2x damage of the pitchfork.
Anyway, that's the deal with Frezy, or at least it was when I was playing my berz. I soon quit playing him after around level 28, so you might get a better informed answer from some of these 65's floating around ;) I'm not sure whether frenzy will fire off more than a triple attack.