> Only r8g (large-memory instances) haver the latest CPU, hence the higher price
No, r8g costs more than r7g. Why would then the others be the same? Ultimately, yes, price/performance of r8g is better than r7g, but not much. When you consider that there was also a Graviton 3E...
m7g also costs more than m6g for example, but the performance increase was a lot higher to make it worthwhile. In this generation, not as much.