> Initialisms are a subset of acronyms; acronym is accurate here.
I believe you have that inverted.
An abbreviation is a shortened version of a word or phrase, and encompasses both initialisms and acronyms. An initialism is pronounced one letter at a time.
Acronyms are a separate special case - an abbreviation that is pronounceable as a word unto itself.
> The broader sense of acronym inclusive of terms pronounced as the individual letters (such as "TNT") is sometimes criticized, but it is the term's original meaning[1] and is in common use.[2]