The Sherman had sloping frontal armor only. Which is good. The Shermans turret was straight sided, although rounded, the tanks sides were also flat and straight. The rear engine area had some slope but not much.
The T34 had sloping armor all around and on the turret.
An rpg clanged off the side of my M60 which had similar/angle sloping armor like the t34 and the rocket went hissing up into the sky. Had it been a Sherman or a Tiger 1 it probably would have impacted the turret. Which would have sucked.
Often the turret is all you can see of a tank target and a flat sided tank is less likely to survive a direct hit or even a glancing blow.
Frankly if I could have any WW2 tank a later model Panther would be the choice.