If you're rushing the M20, it'll hit the field before the pak arrives if you're facing Ostheer as they still need to pull the pios back at some point to build the T2. And a single Shrek isn't a threat for the M20 if facing OKW as it can just push the squad off the field unless a raketen is nearby.
Back onto MG at T0, give USF a mortar instead.
Ain't gonna happen. Why? Because the mortar was pure shit in alpha. If they buff it, it will overshadow Pack Howi, because Pack Howi won't have a special role when a good mortar is available. So the simplest solution is to never mention the mortar. You don't know what you're talking about, let Devs release buggy patches an do not interrupt them. #SarcasmDon'tGetOffedned.
But seriously, a mortar with a defined role will be great for USF and UKF. We won't see one for ULF of course, but maybe for USF.