It's not that deep. Just like GP104/GTX 1080 does not have the physics of a high end GPU, something like Hawaii/R9 390X doesn't have the die size, power consumption, thermals etc. of a midrange GPU.
I know, but that's exactly why these rebrands are so bad.
Well, I'd personally say pricing is the defining factor. Heat and power consumption are definitely not defining factors for a market segment, but a large enough mismatch can be crippling to a product. It will also eat margins at some point. I don't think Fiji is suitable for a midrange rebrand for example.
Yeh, that's just ridiculous but to be expected when you clock an SKU to the moon (also happens when you overclock + overvolt a normal GPU, which is pretty much what RX 580 is).
But I named Fiji in particular because the manufacturing cost of Fury would be unsustainable at a much lower price point since it has HBM and such a huge die. The frame buffer would still be okay for midrange and TDP would still be a lot better than when they rebranded Tahiti and Hawaii.
Isn't Fury already pretty much EoL?
Yes, dynamic/switching power consumption is proportional to the square of the voltage and scales only linear with the frequency. With less heat created, static consumption also drops exponentially and actually also improves switching speed/driving current.
I imagine that AMD & AIBs had to maintain a certain safety margin so that the bulk is still stable.