Are vowels really important for BSL users?

As you know, vowels are more speech sounds rather than written or reading form. I have been thinking alot about vowels.

For hearing people, saying 'a apple' does not sound right but for Deaf people's BSL finger-spelling? I don't mean Signed Excat English, its about finger-spelling. Vowels is really English. Mmm?

Who created vowels in BSL finger-spelling? Should we keep these five finger-spelling despite our fighting for BSL ownership? Otherwise avoiding some hearing people embarrassingly admit they know BSL at pubs - A-E-I-O-U!

Also I asked a hearing person why we often use 'an' for 'hour', she said when saying 'hour' would be sounding like 'our'. Interesting but not for BSL?