The transfer is for every 4 muni you gain 1 fuel, for the amount of your half muni income, yes? This is 25% conversion rate, i dont like, Puma itself use smoke for 30muni, the target weak points(or some other named turret paralyzed skill) is 45 muni, mines, nades, schrecks, g43, flare, off map artys, buff abiltiys etc. comes with muni too, i dont think, everyone, everytime use this transfers...
OK, now i get what you mean, i had trouble the first time
With puma I beat sherman in like 80% cases, depending on howe good opponent is or did i flanked him or he flanked me, but usually puma will fire few shots before it's near dead and then smoke pop out and back to base for repairs, it happened to me to lose puma when I flanked 2 sherman but even then i killed one and left another with 5% hp.
About economy... OKW has 100% muni and 66% fuel, when it transfers muni to fuel it's 66% muni and 100% fuel, while OKW doesnt need so much muni (only shrecks are expensive) then nearly everyone gets 100% fuel.
Ok if you feel Puma wins 80% of the time, then yes, something is wrong.
About conversion, again a few numbers problems:
After conversion, it is 50% ammo and for fuel it is 66% + 1/8 of the ammo production before conversion, which (depending on the map ressources) usually means around +7 fuel, and according to my estimations, makes ~80% fuel income when compared to other factions. That puts the Puma at (70 + 70*0,25 => 87 fuel). So ok it is cheaper than sherman, but still rather costly, if u consider that the Oberkommando players gives up 50% of his ammo.
PS: if you factor in teching costs, then the starting fuel of the Oberkommando player covers up for T3 tech, but the cost of the unit is still ~87-90 fuel afterwards, so only the first Puma may seem underpriced.