You keep bringing up doctrinal USF tanks vet 3...
Maybe you should take a look at how vet 5 P4s absolutely ruin infantry and hey why we are looking at this vacuum why not elite armor HEAT shells where it clubs 76mm Shermans too and drops arty on AT guns too.
If 76s rolled out at vet 3 you would have a point, but they don't and their pretty hard to keep alive that long unlike axis armor.
No, you can't do this, because the moment P4 drives on the base sector from being produced, it blows up to jackson instantly, while USF tanks are imprevious to any kind of damage while having 100% accuracy and no scatter, that's why USF tanks are always and only to be considered at vet3 and why P4s can never be built due to being magnets to jacksons shots, regardless of where both of them are on the field.