I don't exactly see how that is a major issue, considering that heavies come so late and are effectively countered by cheaper, dedicated TD's.
Are Heavy Tanks really that powerfull in 1v1?
Yes they are super powerful in 1v1 and 2v2 simply because of how easy it is to use them effectively. It's much much harder to use multiple medium tanks + support units and keep them alive than using a single heavy tank + support units.