There is sadly no gunshield or way for the MG to not be floating but I'd rather that than a 30 fuel and however much manpower taxi that can't vet or reinforce.
The Mech Assault doctrine already features a Panzergrenadier squad inside the 250 HT, just not upgraded so yeah, an upgraded Panzershreck squad would do the job in my opinion, it would bring sweet memories for me chasing down Allied tanks back in my PE days of playing competitive in CoH, cancerous, but good times.'
I actually thought a bit more about the 221 and I forgot that they actually added a 28mm AT Rifle to it in real life, so it's possible that a variant or an upgrade for the 221 could be made to incorporate both the 223 and 221 armed with the PTRS acting as the 28mm AT Rifle alongside the base version and 222.
Something similar like what eliw00d did to the 250 can probably be done here as well.
It might be possible to replace the MG in 221 with an AT rifle?
Or if it's possible to make a 250 with MG, a 250/10 with an AT rifle should also be possible