it should be 150 base damage plus bleeding...

What's the normal damage

what are you talking man? they hit for 150 Basedamage (multiplied by Melee %), thats 2.5x a Rex does. So how do you come to the idea that they hit for 20 damage?
It doesn't matter how you turn it, a giga can't hit for that damage unless you have a heavy armored target. (Like Turtles 20% Damage on Schell-Parts)

I was hit, with armor and stuff for about 80ish direct damage (not accounting the bleed) from a 50ish Giga. And thats reasonable.

Some of the people that where complaining where over exaggerating the lack of damage due to their dislike of the mod. I never went and tried to get eaten by one but now realize they were full of crap.

Glad this was resolved. :P If people liked the vanilla gigas they probably won't care for this. Though the damage between a vanilla tamed giga and one of these isn't that large. Especially if points are being put in to melee. Since vanilla ones lose 70% melee damage on tame and get less out of points put in to it.