ML20
I'd think trialling a small buff to the LEFH together with a small blindfire nerf for both howitzers would be preferable to nerfing the ML20. Counterbarrage has always been pretty underwhelming, and if it's within scope giving the LEFH a small stat buff (ala ML20 extra shells at vet 1) to accompany counterbarrage at vet 1 would be interesting.
Larger scatter into FOW would be the most direct counter to blindfiring into bases, and further incentivize shooting units on the field in concert with other attacks. I wouldn't go overboard with a nerf in this aspect though.
Mortar pit
I understand the problem with allowing base pits. It's not a problem I have an answer for; I wouldn't restore the ability for base emplacements.
I'm not sure why the new iteration of the mortar pit is so resistant to antitank fire. It feels to me quite counterintuitive [pit is now immune to lategame vehicle dives IF vehicle has no machinegun eg JP4.] I see why target size is that small (to reduce vulnerability to AT guns) but perhaps this could be moderated in a way that allows vehicles up close to reliably hit it while reducing the effectiveness of 60-range snipes.
It's about having alternatives. It's also about having an early tool you can use to take down high received-accuracy infantry on maps where you can't or don't want to rely on the sniper. And it's also about having a vehicle that can move that can do that.
It's an alternative, but speaking from ingame experience in 2v2 and especially 1v1 it's an alternative that simply needs to be more attractive in some way to be useful and competitive. 1.0 showed that a performance increase was problematic, live game shows that the Ostwind is rarely used for various reasons. Hence, my suggestion to try a third tweak i.e. cost reduction and / or improvement against light tanks.
Either way, it's not an early tool to counterharrass- it's a solid mid-late game vehicle built after other T3 vehicles establish a comfortable safety margin, since it's never built first from T3 unless the game is pretty much won already. A cost reduction would allow it to fit more comfortably into this role, and increasing penetration would make it a solid first-build choice against heavy light tank play.
Other observations from further games:
LeIG barrage is very reliable at hitting crewed weapons and infantry with the AOE changes. Not sure if it's a little too strong at the moment.
Pack howi performance is very good. With cost reduction I suspect that they snowball a winning game a bit too well, but at the same time they need to be good since USF has no proper arty lategame besides Major. Perhaps adding a small fuel cost (10-15 fuel?) would differentiate it from the mortar, would thematically be in line with how the full-size howitzers and Land Mattress have a fuel cost.