The issue with running a heavy off of last is that your combo ends up with a heal sponge that can be completely outrotated and your flank can just get completely crushed (as long as the heavy is being spammed well enough that he doesn't just get to walk in). Even if you win the mid, assuming the enemy team didn't just feed blindly into the heavy, how do you get him into second without just getting mega-flanked? I think it's nice as a once in a while surprise play thing but it's something that's hard to pull off consistently because it's extremely counterable if you know it's coming.
The one strat I do think was pretty effective with it was when the old french teams would run a heavy and sniper to gully mid through big door. That's mostly because any time you're trying to peek to spam the heavy, you have a chance of just insta-dying.