What the player in question told me was that the 10 man Skinks are no problem and actually really poor screens, from his view. When Mega-Gargants charge they can put out MWs, then take the monster action for even more MWs, so in average they kill 7-8 skinks on the charge alone, and they do have a shooting attack to kill even more to clear our screens. Also because of their rules they can charge over the screens to the targets in the back.
I think the same way about how to put them down. A Starseer is sooo good with his 24" range spell, and then multiple Salamanders and 1 Bastiladon could roughly do the trick. A fully buffed up Skink Chief roughly kills a Mega Gargant alone, but that is shooting and then Melee with 2s to hit and wound, rerolling 1s to hit and the extra Attack from the Asterisk, Command Trait and CA. Even more important is that a Skink Chief with Mystic Shield, All out Defense and the Crest survives the return attacks from a healthy Gatebreaker Mega Gargant, which are the ones best against Monsters.