You know, if you had somebody put enough hours into learning the mortar's range and drop, merc-mortar could be an extremely deadly combo.
And I have to disagree with the sentiment that the mortar was better than the flak in 1.2. Before the reload the flak does more DPS and can destroy all but two ships in four shots (with a buff). So in 1.2 it was really better to have a flak, since it could kill everything but the Goldfish and the Galleon quicker than the mortar (and considering the Goldfish's hull rebuild, it was probably better against that too). But now with the reduced clip size of the flak with heavy clip, combined with the mortar's new AoE and turning speed, I think it gets the edge.