Well, that's just it. You don't saw a block of wood to make arrow shafts, you use suitable wood that is already long, thin and relatively straight, picked green and then straightened when necessary, usually using a heated soapstone. See
this article for some details about arrow straightening.
The hard part about making arrows is the arrow heads. I could easily see any competent archer retrieving broken or splintered arrows after a battle just to get the arrowheads back. If you have to forge your own arrow heads, IMHO the 4-day lead time in the official crafting system is fully justified, but you should be able to make a lot more than a batch of 10 in that case.
Of course PF2 operates at a level of abstraction where the player doesn't need to bother with the accounting work of keeping track of various materials. You just spend the time and the cost and voilà.
So what is needed for "simple" crafting is both a system for foraging for materials, and a system for time spent crafting that doesn't require the 4-day lead time, when you're crafting something that costs a few silver pieces or less to outright purchase. Personally, as DM, I would allow any trained crafter to use the "earn income" table to produce such items directly, since the offical PF2 crafting system is really designed for high-ticket items like magic gear.
But, again, as things stand there is no official system for crafting low-cost items or bypassing the 4-day lead time.