If you look upon the replay the op posted i would say nearly all your counters are not effective. Let start with the mortar. Its completely rng dependant and if you say your strat should not resolve around luck. The sniper will take a full 30 seconds to bring a maxim to 1 man force a retreat. that is a long time not to mention you are using a very frail unit and one fuck up and you can say goodbye to your 360 mp investment.
The HT strat works provided he doesn't have AT or guards.
But the biggest issue with the maxim is how cheap it is to reinforce. even if you hit with riflenade or a sniper or mortar you virtually cause no mp damage what so ever. this issue can be easily resolved if we double mp cost for reinforcement making the soviet player pay dearly if they use maxim spam.
Mortars are still reliable at killing off weapons teams, you must never use them to think RNG will fuck you over that bad.....
The sniper just like in the video will rack up a huge number of kills, if you fuck up and loose it that is your fault just like in the original, there will not be any soviet snipers to counter snipe so I see no reason your sniper will be in huge danger. It is a well worth it investment, I guess you just must never use them.
If there are guards (like one unit because there are a bunch of maxims and soon to be Zis to stop tanks) then use the sniper to force them to retreat, and use the 222 / half track where the guards are not, they cannot be everywhere.
If maxim spam is a problem for you go strait to the counters and stop just running strait at them. Because rifle grenades are a thing dealing with maxim spam is WAY easier than dealing with the old instant pinning mg42 spam.