The composition of the SERP decides how much a ranking is worth. Position one on a clean page of ten blue links captures roughly a quarter of the clicks; the same position under four ads, a snippet and an AI Overview can capture a fraction of that. This is why any traffic forecast has to be built from the SERP as it actually looks today, not from a generic click curve.
SERPs also differ by device, by location and over time. The same query returns a map pack on a phone in a city centre and none on a desktop two hundred kilometres away, and Google reshuffles result types continuously. Checking the live SERP for your head terms once a quarter is the cheapest competitive research available, and it regularly changes content priorities more than any keyword tool does.