I haven't found shift clicking to overly micro intensive at all. In fact I shift click my squads around my base while they are reinforcing so they automatically head where I need them when they are done reinforcing. ~1 lap around the base for ~3 squad members. It also seems to work well for dodging mortar fire while capping which is why I recommended it. If it's too much for you then that is your problem I guess.
You don't have to use the flame barrage, but the MHT can apply pressure to the 120 and keep it moving. The 120 is only really effective if it can remain static for periods of time. With the high mobility of the MHT it can be constantly on the move harassing the 120 and forcing it to move. Or at least I haven't had much luck using the 120 to fire back on a MHT if the MHT got the first couple shots off. Odds are the MHT will land the first hit if it gets to fire the first couple rounds. I'd have to check stats later but I don't think there are huge discrepancies between their accuracy and damage.
Shift-click-capping works to dodge 82mm shells but the blast radius of the 120mm shells is too big so it makes no difference.
Also, when I'm in an engagement I have the choice to remain in cover and so taking the risk to get wiped by the mortar or move around constantly and lose my advantage towards the enemy inf.
The problem with the 120mm is, that it is a 1cp 360mp unit that reliably oneshots full health inf squads across the map.
Let's take langreskaja for an example;
Park the 120mm in your base and it roughly covers 2/3 of the map. The MHT needs to drive up to the height of the middle vp to even get in range... And between you and the mortar usually lies the whole bunch of soviet troops.
I hate this idea that somehow germans are constantly starved for munitions. Germans have OPTIONS! It is a completely viable option to not buy upgrades and save for abilities and doesn't leave you at any disadvantage to the soviets. The soviets don't have that option and can mostly only use it on abilities, it's not as if they have more munitions.
So what do you suggest? To fight without using rifle nades, lmgs, bundle nades, tellermines, FHT, flamethrowers?
Soviets do not have more muni, but their abilities cost way less, that's the difference.