> How do you properly measure this?

The same way you measure utilization and cost at a customer level.

I can name at lest three companies where their biggest clients are also the bulk of their costs - they lift revenue but drag the margins. I can name another couple who spent years marking their products entirely wrong because they simply had no clue how their product was really being used.

> Is the feature only used on some rare data that is uncommon but still can occur?

This is where the competence of your product team comes into play. We're building features faster with AI but none of it is moving the needle. That has little to nothing to do with code quality, and everything to do with product teams.