Agents locate controls through the accessibility tree, where a <div class="btn"> is not a control at all. This is the single most common reason an agent gets stuck on an otherwise ordinary page.
Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.