You are comparing a fully upgraded finewood bow to a lv1 huntsman bow which obviously makes the huntsman bow look bad. When fully upgraded it has the same durability and 10 damage more. It's normal in Valheim that a fully upgraded thing from the previous tier is about as good as a non-upgraded thing from the current tier so why should it be different with bows?
For a lv4 huntsman bow you need a total of 80 iron which is 1-2 crypts depending on how big they are. That is not expensive considering the cost of other iron based gear.

That said, you are never forced to upgrade your gear and can continue as long as you manage to survive without better gear.