In the vast majority of 4v4 maps it is practically infeasible to reach and destroy a howitzer. Thus, having abilities that act as fail-safes for that is a good design. Adding brace-like abilities, or removing this OHK feature could lead to cancerous plays.
For instance, Mortar Pit sim city is cancerous because it doesen't die early enough. However, howitzers make short work of it. Thus, there are some balancing checks there. However, if howitzers themselves become unkillable, why not build 1-2 of them EVERY SINGLE GAME?
The changes in off-map abilities mean that no ability below 200MU can insta-gib howitzers anymore.
Furthermore, changes to howitzers means that when the howitzer dies, it's no longer 600MP (hard to replace) down the drain.
So yes; the first time you build a howitzer, expect it to get blown up like before. Follow-up howitzers will start putting a strain in your opponents' munition reserve and should be able to survive for longer.
I have always wondered, why not simply make arty barrage costing munitions and reducing its building price (for example your DBP price cut in half for each arty unit). 100 munitions per barrage for any arty unit (including the priest).
In 4vs4 the guys building Arty is also the one building fuel cache for his mates, with this cost he will be forced into splitting cache in fuel and munition.
This change would strongly reduce the arty spam in general. Arty player would have to use more wisely their piece of arty, when and where to strike and not simply click the barrage button every two minutes. Opposing players would have to decide if they want/need to hard counter arty or leave it as it is.
Reliable Axis -counter option ( able to one-shot ML20/B4)
Ost:
3 SDB commander with recon(SCAS, Luftwaffe, Elefant)
1 SDB commander with both lefh and SDB
1 fragmentation bomb commander with recon
OKW:
zeroing artillery
assault artillery
Reliable Ally -counter option (able to one-shot LEFH):
SU:
1 IL-2 bombing strike commander with recon( basically no one would pick)
It appears axis have more reliable counter option in commonly used commander. So most of the time, the availability of using munition to reliably safely clear the enemy's cancerous howitzer play is only on axis side.
You forgot USF mechanized commander, reco swip + 155mm arty barrage wreck every piece of artillery.
But you are right, there is a lot more reliable commanders on Axis side to counter static arty.