Boy, this is a tough one to crack, mainly due to the way these units perform across modes.
Some people on the balance team are advocating for final tier side tech as a more equitable solution than tying heavies to all tech buildings etc.
Do people like this proposal?
Also, what (if any) further nerfs do people think would be needed in conjunction with the above?
i think this is the best solution brought up so far, because you can adjust the timing for each heavy individually by both the price of the upgrade and duration it takes to complete the final tech.
i'd also advocate against nerfs in the performance department except fixing the (maybe?) bugged scatter of the tiger. heavies should pack a punch against all targets and i'm glad they finally do across the board.
this, however, doesn't mean they aren't currently overperforming, but there are a couple of other areas that could be used to tone down their impact to reasonable levels.
1) the price could be adjusted to better match the performance, say, by increasing fuel costs by 15-20%.
2) repair times could go up by tweaking hp values and received damage modifiers accordingly. this would keep the overall durability unchanged, but reduce the field presence of heavies noticably unless you invest in an army of pios/engineers to compensate.