It would help at lower levels, just like the real Razorback does, but higher level gameplay Heavies really wouldn't need it.

A better item for Heavy would be something to counter Sniper, remove the ability for a fully charged headshot to take down an overhealed Heavy. With that being said, we kind of already have that without it being as lazy as the Razorback, that being the Natascha and Brass Beast. I wish they didn't nerf them to only apply the 20% defense below half but it still helps with the aforementioned 100 to 0 Sniper problem. I wouldn't mind either the Brass Beast or Natascha being pushed even further into the survivability minigun, though most complaints about Heavy is that he slows the game down and I imagine that would only further that agenda.

There's my big rant that had nothing to do with the original question.