As far as special wallbreaking, Mega Camerupt can definitely do that too, albeit with a bulkier inclination over a faster one. I'm seeing a lot of talk about using M Camerupt on a Trick Room team, but I haven't really seen anyone mention the kind of damage output it can get under the sun. For demonstration purposes:On the other hand, none of the new Megas can really do the whole "specially offensive wallbreaker" thing garde's got going for her (if anyone says glalie I will actually kill them), Mega Diancie does sort of come close but her Moonblast isn't quite as good as Garde's Hyper Voice, doesn't get Will-o-wisp/T-wave... I expect Garde to go down in viability, maybe even to B+ or A-, but she's still got a relatively unique role.
252+ SpA Sheer Force Camerupt Fire Blast vs. 4 HP / 252 SpD Blissey in Sun: 268-316 (41.1 - 48.4%) -- guaranteed 3HKO after Leftovers recovery.
So, while Blissey and Chansey do wall it, they're just about the only things. This thing's in the same vein as sunboosted Darmanitan and Victini, but without crippling recoil/statdrops and is actually neutral to Stealth Rock.