That's what I'm thinking - they make trade-offs to reach peak performance in desktop designs that don't translate optimally to laptops and when you start from mobile designs you probably made the opposite trade-offs - that would be my guess for the discrepancy.
Laptops vastly outsell desktops, so this tradeoff means hurting the majority of your customers to please a small minority. Servers also care about perf/watt a LOT and they are the highest profit margin segment.
Why would AMD choose a target that hurts the majority of their market unless there wasn't another good option available?
The architecture started in desktop space and data center/mobile was an afterthought up until Intel shitting the bed repeatedly. If they redesigned from ground up they could probably get better instructions/watt but that would look terrible if it wasn't accompanied by a perf boost over previous generation. Just like Apple doesn't seem to scale well with more power.
