I agree that "frontier model" really does mean "pushing the frontier of intelligence", so Fable or Astra.

They might mean the intelligence/dollar frontier aka the Pareto frontier, but honestly much of the time that's not a great measure.

If you are doing repeated work on the same task (eg call center triage) then you can always beat a large LLM on price by fine tuning a small one.

If you are doing knowledge work then models are so varied that factors other than price are usually important. For example, lots of people moved away from Opus 5 because of it's awful English, whereas Opus 5.5 has fixed that. These things aren't measured in benchmarks.