yes my GS is currently 6 star and 51/100. I figured he would be useful. I been wavering to go with a squad of lando 7* lead (or boba fet), sth 7*, biggs 7*, boba 7*, and wedge 4*.. OR to put my GS in the place of Wedge. i played around with it a tiny bit and had really mixed results. might need to keep experimenting with either him or GQJ who is 5* still.
So my current plan is to finish GS and then do what you did with finishing off the mod battles and doing the mod challenges (i had tried the mod challenges 5 dot a few times with no success which is part of the reason i went back to farming GS).