I suspect not, and I'm being dumb, but ...
Usain ran quickest.
is parsed (https://corenlp.run) as
NNP VBZ JJS.
Why JJS (Adjective, superlative) and not RBS (Adverb, superlative)?
Using extended dependencies I get
dep: advmod, dependentGloss: quickest, governorGloss: ran
yet the manual (https://nlp.stanford.edu/software/dependencies_manual.pdf) says
An adverb modifier of a word is a (non-clausal) adverb or adverb-headed phrase that serves to modify the meaning of the word
Would be very grateful for an explanation of where I'm going wrong.