Think about it this way. Both sides have good SMGs, but people rage about the MP40 a lot more than the PPSh because the MP40 is more straightforward. You can hit with it accurately at a good range, it's more versatile, and it's more in-line with how guns in other games handle. Does this mean the PPSh is worse? No. It just requires a different set of strategies to play well.
Same thing with the PIV v T34. People expect tanks to be unstoppable lumbering monoliths that plug away at each other from range, but this isn't the case with the PIV/T34 matchup. The PIV handles like tanks in a lot of other games, a big, hard to kill, lumbering monster. The T34 is light and fast, with less frontal armor and a smaller gun. Just because you can't match the PIV blow-for-blow in a stand-up fight doesn't mean that it's impossible to win with the T34. It just means that the PIV is better at long range, stand-up fights.
My first time out on Grumrak, I scored 4 PIV kills not because I'm some uber tanker (this was my first time behind the controls) but because I knew how the T34 matched up against the PIV. I got in close, hid amongst the buildings, and then quickly circle-strafed the PIVs and spanked them in the rear before they could draw a bead on me.
A lightweight can beat a heavyweight boxer, he just can't use the same "punch him in the face till he falls down" strategy that the heavyweight can.