Expected click-through rate moves with the ad itself. Headlines that repeat the searcher's words, a description that names the offer, and assets that give the searcher more to click all raise it. So does pruning. An ad that shows for searches it does not answer drags its own expected rate down, which is why the negative keyword list matters as much as the ad copy.
Ad relevance moves with structure. Keyword groups built around one intent each, with the ad written to that intent, score well. A group holding forty loosely related terms and one generic ad does not, no matter how good the ad is.
Landing page experience moves with the page. The page has to load fast, answer the query above the fold, and give the visitor one clear next step. It also has to be honest. A page that promises something the ad did not is abandoned by the searcher before Google ever has to notice.