Even so, among a pack of dogs, GIS is a real woofer.
I remember doing some quick napkin math back in the day, comparing the various high DMG ST attacks of various Tanker sets, comparing them by DPA. GIS was just way the hell down there, last by a mile. IIRC, I calculated it would need about a 90% boost to its base damage to get to the median DPA value of that set of attacks. If at the same time, you shortened its animation to use the one from Icy Assault's "Ice Slash" (that set's unique replacement of GIS), the mount you have to buff by drops to about 45%.
(Don't hold me to those numbers, that's to the best of my recollection of some Excel doodling I did 7-8 years ago while bored at work. 🙂 )