Totally untrue. Luna and Sonnet 5 are very comparable: https://artificialanalysis.ai/#intelligence

Luna is an extremely strong model.

In my real world use Luna is as useful to me as Sonnet. And it gets stuff done faster and follows my instructions more closely.

Anthropic basically downgraded all their tiers when they released Mythos, no nah, Sonnet 5 is the successor to Haiku 4.x