The pakhowi already doesn't OS any full life squad so your first paragraph is out of subject, what you're proposing then isn't going to make its detractors happiest since it will be subject to kill more wounded models per shot. Low health squads are going to suffer much more from your change.
Again the pak howi cost the same as an elite squad and is perfectly and easily counterable by any kind of combat units, so I don't know why it shouldn't have the same killing power as such. From this reasonable point of view: or effectively you want to make it a real howitzer on barrage only and thus give it the firepower associated to it or leave it on AA mode as it is today. On both cases you'll meet people unhappy about it and just want it to be nerfed to oblivion.
This is essentially my take as well. Slow but consistent damage by autoattack or a much more useful barrage are the only way this unit stays effective.
Balance options, if we absolutely have to balance this shit:
1. Nerf/Remove AA,
but make the barrage deadlier and/or cool down faster (
more shells is not a solution, as this would only of practical use versus buildings like the OKW trucks. Imagine if the Zis-3 barrage was twice as long but did only half damage; nobody would use it despite the same theoretical damage output)
2. Jack the price up to 400~ or so but make no other adjustments to the unit itself; one pack howitzer isn't going to be killing squads unless the axis player is braindead, and this way two pack howitzers is an even bigger investment than it already is. Note that the price of this unit before the crew reduction was 380 or so and people didn't bitch about it nearly as much.
3. Minor changes like increased setup/teardown times to make it harder to evade call-in strikes/counterbarrage, autoattack kept more or less as is, maybe a slight price nerf, maybe a very slight scatter increase to autoattack if that gets touched at all.
4. Keep the pack howitzer exactly as it is, but maybe buff ostheer counterbarrage to make axis idf a more effective counter. Either way the panzerwerfer's counterbarrage range is way shorter than normal and should probably get buffed anyway.