Related, this ngrams seems to indicate that the words dactyl and spondee occurred more often between 1800 and 2019 than did iamb, which doesn’t seem likely. And even more improbable, this one makes trochee out to be more popular than iamb. Hard to figure how that could be so and one wonders, too, what might have made dactyls so popular in 1971?
On the other hand, the phrase iambic pentameter has been on a tear since 1800 — here’s a chart contrasting the occurrence of iamb against iambic pentameter.
.i`` * ^ / . . . . . ` `~ 