I can't really see them doing that without breaking the thematic element of it. Your retainer is ostensibly an entirely separate character in the world from you, and it doesn't really make sense for them to spontaneously be a highly experienced archer having never picked up a bow before just because you are.

That being said, the reset on any class change is harsh. I would happily support a change where they:
1. Cap a hunting retainer's level based on your highest DOW/DOM level even if you don't have that particular class at that level (it's not like you're out there mentoring them on the finer points of archery while they're exploring), and/or
2. Let retainers keep their levels when they change jobs (I don't forget how to be a paladin when I pick up a pickaxe; why should my retainer?)