That's not correct. AWS sells Graviton 3 based EC2 instances at a higher price than Graviton 2 based instances!
For example a c6g.large instance (powered by Graviton 2) costs $0.068/hour in us-east-1, while a c7g.large instance (powered by Graviton 3) costs $0.0725/hour [1]. Both instances have the same core count and memory, although c7g instances have slightly better network throughput.
I believe that is pretty unusual as, if my memory serves me right, newer instances family generations are usually cheaper than the previous generation.