I've wondered about this, too! But I only have barenia watch bands, so haven't concerned myself with it too much. I would love a barenia bag at some point though, as I love its casually elegant feel. Some of you likely remember the original
Coach leather of the 70s and 80s? I remember it being very similar to barenia, as it was a gorgeous, thick, oiled leather, and it slowly developed a similar patina. I didn't wear my Coach bag from that era in the soaking rain, but didn't really baby it either. I never treated it with anything, and it aged beautifully. I do think oiled leather is inherently somewhat protected. ETA Haven't heard much about the new grained barenia faubourg, also wondering why it would behave differently than regular barenia.
For those interested, I'm posting a link here to hermesgroupie's excellent reference thread on the various types of leather. She notes that rain drops evaporate on barenia, leaving it unharmed.
https://forum.purseblog.com/threads/reference-hermes-groupie-s-leather-book.49095/