i don't think it's broken but i think it's unfair that the axis, who generally have the better tanks, are the ones who can get tank smoke on all their vehicles. it gives their tanks, which already have higher survivability, even higher survivability while the allies end up bleeding tanks in a game about unit preservation.
Well, German tanks DID have this ability. Check out the picture below in Band of Brothers where it is being used:
Also, British tanks have doctrinal smoke as well, so your assertion axis are the only one with defensive smoke is incorrect.
One last thing. Shermans did indeed have White Phosphorus rounds. One of the uses of this was to shoot it directly on to German tanks where it stuck and burned for several minutes obscuring the vision of its crew (essentially blinding them) until the German tank could be dealt with. Would be a cool ability actually.