I'm not sure that is accurate for Gravaton3, which appears to be besting intel/amd in a number of cases. So, it doesn't appear there is a clear leader between the amd, intel and gravaton instances. Meaning everyone should be benchmarking their application and picking one.
Amazon here seems to be leading the Arm technology pack, as they are using a newer generation of CPU, while arm instances on other providers tend to be providing gravaton2 (Neoverse-N1) based instances. I would imagine that gradually changing in the near future as those vendors also upgrade.
ARM isn't the optimal solution for every application at this time, but anyone who isn't seriously considering it probably needs to update their information.
The big savings on graviton come from no hyperthreading. A VCPU on x86 is a hypercore, but a VCPU on graviton is a full core. So you get a full core and its L1 and L2 all to yourself. Usually for cheaper than an x86 VCPU.
https://www.phoronix.com/scan.php?page=article&item=graviton...
Amazon here seems to be leading the Arm technology pack, as they are using a newer generation of CPU, while arm instances on other providers tend to be providing gravaton2 (Neoverse-N1) based instances. I would imagine that gradually changing in the near future as those vendors also upgrade.