the old a320 boards have shittier vrm and small bios size and poorer dram setup.
amd is only protecting you.
Yes and no... The 5000 series is quite more power efficient compared to the 1000 series, which is what the A320 boards were for. Maybe the 16C CPUs are overkill, but both the 6 and 8 cores should definitely be fine on any decent 300 series chipset board.
It has more to do with logistics more than anything. And obviously the motherboard partners prefer to sell new motherboards rather than needing to upgrade their old ones without any additional income. So AMD needs to find the balance between keeping their customers and their partners happy.