Note Amazon doesn't specifically care about perf/watt. They care about total cost. Last I read they can acquire a given level of compute for about ⅓ the cost of AMD. This is fixed, but a meaningful sum. They also have to pay for the electricity, the land so compute/rack is a factor, there's other factors in there in terms of their ability to control and monetize it, so one of their big applications for ARM is Lambda which is a very heterogeneous compute environment that isn't even well mapped to individual cores and has all kinds of additional transaction cost to isolate that process, etc.
So I wouldn't even expect Graviton to have particularly similar design constraints to AMD. The whole point of AWS was to rethink the cost model of traditional compute and that should apply not just to datacenter and racks but also the die itself. To them the superiority of ARM isn't to run a bigger Crysis, but to enable that different cost model of compute. Apple is doing something similar but rethinking how compute is delivered. Every x86 benchmark is on desktop, but you can switch most Apple Silicon benchmarks to a laptop with a fan and you'll get basically the same number. FFS, an iPad was atop the leaderboard for half the year. A big part of Apple's market is you can take your 9950X3D performance to an airplane seat, to the hotel room, to the conference. And if you can live with slightly less performance, you can put that in your pocket. So are they trying to win on desktop? Not really. They don't want to be behind, but that's not where their money comes from. Their money comes from continuing to eat away at the desktop PC market, which again peaked in 2012 right when the iPad launched and knowing they can easily win in portables and below.