Well I have also struggled a lot with mg42 into fast FHT.
I started going 3 cons tier2 instant field gun, no molotv or at nade and using my early munitions on arty ability to clear or force retreat the mg42.
I then get a maxim and the at\molotov upgrades this way you have early AT without having to rely on guards, you can go shocks to fight pgs or just get more cons with ppsh.
If you like you can also rush for t\70 instead of getting the cons upgrades but I feel its always better to get those to protect the field gun's flanks and you will need the upgrades in the late game specially the at nades
If you're waiting till you can use some arty before you clear the MG then you're going to lose far too much map control. You really have to try and work on your flanks, then use that muni's to get some AT nades going, and save the MP you spend on that Pak on another earlier squad of Cons/a support weapon and get the pak a little later, which will mean you'll have more capping power and hopefully be able to take more territory to delay that FHT.
Just my opinion.