The Drivers hatch was basically a huge bullseye to aim for. The decision to mount both the engine and the transmission at the rear pushed the turret too far forward to have a top opening hatch for the driver.
I read recently that the survival rate of Soviet T34 crews was only around 20 to 30% during the 1943 summer offensive
Still, it was better than the M3 Stuart - the hull crew hatches on that wouldn't even stop the German 37mm "Door Knocker", never mind anything bigger...