Regarding exploit, if you mean USF player X leaves his m4 Sherman and then player Y enters the Sherman to upgrade it so player X can have an upgraded Sherman, then I think teamwork should be rewarded. I have the same opinion for the Vickers K drop. I think intentionally blocking teamwork for Vickers K drop and M4 Sherman upgrade is babysitting players too much and limiting creativity. If players have enough coordination to do such things, I think it is a great feature of the game and not a bug.
Well the mod team does not seem to think so think and thus has removed vickers drop in the patch.
I think trying so hard to figure out all the exploits and try to block it so players don't use it takes too much time and is too much babysitting. Things like multiple sturmtiger exploit, or giving WC51 to Assault Sections. There are 1 million "exploits", and I think it is silly to go after all of them. They are rare and unintended features that require exceptional effort and coordination to accomplish.
I think starting production of a weaker default version of a unit to later upgrade
it is the point of an upgrade. Upgrades are for improving the stats of a unit after its default version has been purchased. We purchase a Obersoldaten and then upgrade it with STG44s to make them better. We purchase a Panzer IVJ to upgrade them with commander ability. I think it is intentional.
And you would be able purchase a 75mm dozer Sherman and upgrade it with HMG.
You have not seen a single argument explaining why the Dozer should be an upgrade and not a separate unit.