It's still that way. I guess later some letters started indicating certain vowel sounds a bit more directly, but it's mostly little dots and lines that only get used to teach or are placed on text where ambiguity isn't acceptable.
Also, they transposed the German "J" to the english sounding "Y" at the beginning of "Yahweh" but did not transpose the German "W" into an English sounding "V" to match the Hebrew letter. They should either have it as JHWH or IHVH but instead we get a mix-and-match.
vav can do different stuff depending on context too. not sure vav as a vowel indicator is as old as the tetragrammaton? i know some features of the writing system are later innovations - most accomodations to vowels don't go back to paleo-hebrew iirc, but the tetragrammaton probably isn't that old anyway.
Anyway if that vav is signalling a vowel, it could be an english o/oo sound, or a lot of things
I'm not an expert, i am just the specific kind of nerd that will slowly learn archaic languages at whatever pace i can manage and i've got subpar hebrew literacy for it, so i don't wanna mis-represent my credentials here.