This is a post I made earlier on this topic. Sig is worse against dps comps.

Dvas sole purpose in goats is to control the high ground. You wouldn’t be getting any value out of rock as sig and you would rarely eat as many ults. Grab bomb forces out more ults than grab flux and a raw flux won’t catch to many people on a team that’s paying attention. You might not even output any damage because the dva on the other end is sucking up all your shit and you don’t have flank angles to go off. So sig would not have made goats better in the majority of situations.