If you want to rework Soviets (good luck with that), make another thread about it.
221 is simple the Obers of the vehicles. It's not meant to stay vanilla and the fuel upgrade is just there as a stopgap.
I wouldn't buff the performance, but would play by moving around the cost to build and the cost to upgrade. Take 5f from it and move it to the upgrade.
If the unit is not getting vet reasonable, improve the range/speed of the shared vet. Want to see the performance when people get access to riegels.
The unit has shared vet. Doesn't need to be on first line to vet.