As soon as you plop a Pokemon dead with Fire Blast, Focus Band Infernape can Revenge Kill Heatran with Close Combat. Lol at needing maximum power to do unnecessary overkills. Timd w/Life Orb or Scarf is the way to go.
You've been told again and again... Almost any Standard Pokemon faster than it is a counter. If it then has a high power attack that is SE against Heatran and isn't Water-Type, it's a counter. There's plenty of those.
Honestly who use a focus sash or Focus banded Fire Monkey.You make the combo sound like horrible thing,Both pokemon by themselves work well they don't need each other to successful,but together do have some mutual benefits that thread mentions.You can easily abandon ship in setting up the process,with out hurting your team.Also Sleep Powder will end up being the the prefer choice on tangrowth,if you can't deal with put it to sleep.
No two poke will cover thing it always about that third and fourth pokemon and me personally i am all about trios and quintuplets.Seriously add CSmence to mix does that now look better,Heatran and Tangrowth are good foundation to build a team around.