Two facts:
-The Mobula can only get two mercs on one target due to the gun's low maximum yaw. There is no ship in the game that can get more than two mercs on a single target at any given time.
-The number given on the Wiki for the Squid's hull are wrong. It has 850 hull.
Then just turn the Mobula like Leonardo da Vinci's cannon tank thingy and fire them separately. While this will increase the time it takes to fire all five mercuries, it's probably still incredibly fast. I'll do some testing on this tomorrow.
And even then, being able to remove the armor of any ship at long range within a very short of time still seems pretty frightening.
But now that I think about it, I still need to know if damage multipliers are multiplied with each other (i.e. 100base*1,3chargedrounds*1,2bufftool) or just a percentage of the base damage of the weapon (i.e. 100base+100*0,3chargedrounds+100*0,2bufftool).
Also I haven't done anything accurate regarding actual hull damage, I might need to do that sometime.
Anyways, if we take the base damages of 75 and 300 of the merc and calculate the final damage dealt with percentages of the base damage and with damage modifiers applied after all the other damage bonuses, we'd have
(75+75*0,3+75*0,2)*1,5+(300+300*0,3+300*0,2)*0,2
=168,75+90=258,75 armor damage per shot.
258,75*2*5 would still be 2587.5 damage, which isn't all that far off from 2614 damage.
3 mercuries firing their mags would still be sufficient to take down any ships armor, as they would deal 1552.5 armor dmg.
And turning from the left side guns to allow the middle gun to fire should be even shorter. Now if you take hull damaging weapons on your right and have your left-side gunners run to the right while middle one is firing, any enemy that can't get past you or kill you fast enough could already be considered dead.
Correct me if I'm wrong, but with this strategy a Mobula can kill any approaching ship in a matter of seconds, and anything without powerful long-range weaponry has basically already lost anyways because by the time it has gotten close it has already taken enough of a beating that it needs to retreat, thus forcing the usage of other long-range weaponry, and what would be more suitable for this than another set of mercuries?
I only theorycrafting here, as I don't have any practical experience with mercuries, neither on the giving nor on the receiving end, but this does worry me a little bit.