Here’s my reasoning. Carapace is supposed to be hard armor, a tank if you will. We aren’t supposed to easily deal with them from range. Because they have the slowness and tankiness, to get close to you and pressure you with their bulk and fear of overheads. That’s the game mechanic and idea, I think, of the Crushers, Bulwarks and Maulers.
Veterans can (in my opinion) deal effectively against Crushers with Bolter, Vigilante Autogun and Helbore. All 3 of them does over 2k DPS on Crushers (haven’t checked blessings and perks, some are Carapace, others aren’t). Which is as high as you’re going to get with ranged. Infantry Autogun and Recon Lasgun, with “Onslaught” perk, both do 1200-1500 DPS on Crushers (includes time the stack up the brittle).
So, while I hope that they don’t absolutely obliterate Plasma Gun for those PG enthusiasts out there, I think Veteran has quite a lot of options to deal with Crushers at range .
And if that fails, hopefully your teammates are there to pick up the pieces. (They’re not)