Titles, descriptions and structured data mostly change whether people click a result they were already shown. Measuring that work on position asks it to do something it was never going to do.
The metric a fix is measured on is chosen from the issue type at landing time, so a missing-description fix is judged on click-through rate rather than on rank, and the choice is recorded rather than argued about afterwards.
Try it on your own site, free
No card, and the free tier does not expire — the first verdict takes about six weeks to arrive.