With Nitro they disclosed that every EC2 machine deployed in the last 5+ years has at least one ARM chip because each server has a nitro card.

So reading the tea leaves... the first generation of EC2 ARM (a1) could have been almost as simple as two nitro cards hooked together.

Graviton2 is likely a bigger chip than what they're sticking on Nitro cards, but if Graviton1 was just the overhead for each Intel machine...