One of the problem with the t34 is that by the time you get to tier4 you have ticked the number of command point where heavies are aviable.
Teching to T4 + T34 is something like 170 fuel which you can be tempted to invest into a KV8 or wait 75 more fuel and build an IS2 for more impact than a T34. One could argue that when you build a IS2 you could have 2 T34 and the price of each t34 is reduced for each t34 you build.
Soviet medium fuel cost is 165/175
For comparison:
Ostheer is 175
USF is 155/165
and UKF is 130 (but has a lot of side tech)
So saying they come out the same time as heavies is a huge exaggeration. T-34s come out the same time as all other mediums.