Yeah that's cool except there's a reason why the Cruisers on Seamist are not visible even if you spectate over to the place the shells are coming from. We don't have a model. There's a bunch of other problems too:
That range suggestion means it would have a godly 5-10m extra range compared to the Destroyer... hooray...
A high arc would allow it to hit subs which is totally not what it should be doing. Unless its gun was forced to a high angle which would also mean it would have a lot of trouble actually hitting certain buildings even if it had 100% accuracy.
"Really slow", only 10-20% extra damage, inaccurate, and a negligible range increase... considering that a Destroyer will get in range of the enemy base much sooner and therefore deal damage sooner and can actually HIT aircraft and can reliably hit buildings other than the sub pen, and will ideally not have a dumb arc setup that allows it to hit units that it shouldn't (subs), why don't I just get a Destroyer instead?
It would have to have only one turret for the same reason I've mentioned dozens of times about why the Destroyer's depth charge rack can't be turned.
It's difficult enough for destroyers to navigate the icebergs on Hostile Waters, you really want something twice as big going through there?