As a counterexample, English speakers in India use the word “revert” in email a lot more often than Americans do, because there it can mean “reply”, as in “I will revert with that information later today.” I would think that is a much more frequently expressed concept than any of the other meanings of “revert”, so Indian English (at least Indian business email English) is going to have a higher frequency of “revert” than American English.

Not that this exact phenomenon applies to “delve”, but it shows how word frequencies can vary across cultures regardless of “grade level”.