I was about to say you never felt the bite of Zil's Blender-Galleon, but then I remembered that he used it on your team as well ^^
Against some ships heavy carrorade focus works well, just not against a galleon that has both a LJ and a hawacha (I have been on the receiving end of that build amd I just couldn't outrepair double heavy carrorade armor damage, and then when the armor was down, he just finished us with echidna). Heavy carrorade with piercing could very easily be OP.
Yea hwachas are the scourge of that layout. It's too bad the only recorded use of it was in that match, lol.
I like the shatter on carronades for the small degree of gun destruction you get, like when facing a metamidion. I agree with Mattilald that adding piercing, even if removing the shatter, would make it OP. I mean, at 1.1.5 they had to lower the armor modifier to balance it out.
The reason they aren't as great as the gat is of course because it's not the primary role of the gun, which is fine. Merc and gat will have that advantage, and I think a new gun would be preferable to tweaking the existing armory to that extent.