C6g, M6g, and R6g (powered by AWS Graviton2) each support 8 sizes, along with bare metal. A1 instances (powered by AWS Graviton) have 5 sizes, along with bare metal.
That's a total of 33 distinct instance sizes.
That still leaves storage optimized and GPU optimized instances missing. I'm guessing storage should be easy enough to add, but what about GPU?
From my novice experience with GPUs, they need finicky drivers that must be ported by the GPU manufacturers, so I figure it might take a while to get competitive ARM GPU instances.
NVIDIA is supporting Arm for CUDA development, see https://nvidianews.nvidia.com/news/nvidia-brings-cuda-to-arm... and https://blogs.nvidia.com/blog/2019/11/18/ngc-containers-arm/