So what everyone is saying here is that both Flaks are too weak and the Mortar is too strong.
I'm talking light variants just to reiterate. Maybe the mortar needs spread again to compensate for the added boon it gets from lesmok.
After testing last night, we pretty much gave up using lesmok in a merc in favor of other ammo, as it just wasn't useful anymore.
LJ pretty much comes out equal, though it technically is easier to hit with at range. That also equates to more arming time.
I don't usually use heavy flak. It was always very situational, and unless hull armor is down, it was generally not useful to me. Depending on how easy it is to shoot now with the added speed, I can see one shot being fine so as insta kills don't become a thing at max range. Im talking theory though as I don't use them much.
Tweaking lesmok is like tweaking the gatling for you, essentially, because it is the only ammo type that increases the range of guns, so it's of paramount importance to those trying to use such tactics.
That said, I haven't shot a heavy flak in ages, but I don't remember it being easy. You make these guns with huge range, but without lesmok, hitting at that range is nigh impossible. I get the dance that goes on here though. If you make guns easier to shoot, lesmok makes it too easy. Make them too hard, and lesmok becomes required.