I know OKW have no real counter to the ML-20 but nerfing it with changes such as these is not fair. The size of most 1v1 maps does not conciliate the need of forward placement all of the time. Again, it's a player choice. You aren't being forced to place trucks forward and if you do so, how can you complain about the potential counter/punishment for doing so? If howies were unable to target HQ sectors then OKW players would have a choice of safe placement or opt for forward placement high risk/high reward. But I agree, 200 damage and then maybe 240 damage with vet would be about right for the ML-20.
Except that forward truck placement is entirely how OKW was designed. You start with the least MP of any faction (due to it being concentrated in your starting Sturms squad) and thus your starting map presence is artificially limited. Yes on several 1v1 maps this isn't the biggest problem, but on others it's easy to get pushed right off the field due to the relative power and quantity of Allied basic infantry over your own.
Katyusha's, mortars, ect can all punish truck placement but they don't do it with such high damage and deadliness. The issue with the old ML-20 was that the cooldown was to short to actually get any repairing done while doing repair while barraging would just lose you all your Sturms, so 2 barrages would normally always kill the truck.