That's why I said it represents a vowel by default. Both
w and
y can represent semivowels at times.
As Dobie's video points out, it is part of a vowel ("aw") in many words.
I didn't actually watch the video, but I think this is one reason why it's important to distinguish sounds and the way we represent those sounds. Strictly speaking, vowels and consonants are sounds, not letters. A word like
awl has one vowel and one consonant, despite its spelling.
And even when
w and
y represent semivowels in Welsh, it's always as part of a diphthong, so you could still consider those instances to be part of one vowel.