Talk I'm listening to today: https://youtu.be/EZ05e7EMOLM
The experience of ATDD (acceptance test driven development a la Cucumber Gherkin etc) definitely follows mine. They're a lot of work to write, and the customer-facing part never is used.
To expand: No customer cares that button X opens modal Y. They care about higher level stuff like "does the wizard I asked for exist? do I like using it?"
For a webapp the finest granularity that will be read is page, form or dialog. That's it.