it is better to treat brano as a loanword from some unknown source….
I wander what source would that be? It can not be Slavic as Slavs and Celts according to Matasovic and his follower Ingva could not have lived together…
Have you ever heard of these words ingva

Irish bo
Serbian vo

The Irish word comes from Proto-Celtic *bow-, i.e. from PIE: *gwow-.
It is not the root from which Proto-Slavic *volŭ, our word is a Slavic inovation without Indo-European cognates.

Irish ban
Serbian van

I don't think there is such word in Irish, the PSl. word was vŭnŭ – not so similar now, ay ?

Irish gob
Serbian kov

It should be gobae, don't make stuff up. It comes from Proto-Celtic *goban-.
The slavic word root comes from IE ie. *kow (d), those are two different roots as you can see.

Irish bran
Serbian vran

Our word had the form *vronŭ up until the end of the 8th century. The form vran could only be possible from 10th century. Learn a thing or two.

See any pattern here?

Yap, a  mental one.