I suspect in the sense that 'w' acts like a long vowel or a diphthong in many ca...

I suspect in the sense that 'w' acts like a long vowel or a diphthong in many cases in English when it is used in the middle or at the of a word.

E.g., (spelling vs pronunciation) 'town' vs 'toun', 'own' vs 'oan', 'bow' vs 'bo' or 'bau', etc.

It definitely seems like the most vowel-like consonant after 'y'.

OJFord on Nov 21, 2019 [–]

'Semi-vowel' seems to be the word, for 'y' too.