It seems that I'm not the only one dissatisfied with the Crossbow being the gateway to the Bow. Crafting-wise it makes little sense as I can much more easily acquire the means to make a simple bow that I can to make the earliest crossbow. To make a crossbow I need to have access to at least copper if not iron and a forge and anvil. To make a bow I need a primitive knife, a branch, and a piece of rope. I can gather all that with my bare hands before I've even thought about making my first shack. As far as their use goes yes, it is easier to master the basics of a crossbow, it's why it was such a major breakthrough in warfare for the peasant militia types. You show them the direction to point it and tell them to pull the trigger. Then they learn how to pull it back and drop another bolt in. But similarly, a bow is simple...instead of point and click it's pull and release. So here's my suggestion.
Instead of Crossbows as the gateway make it a skill called Marksmanship. At 0 Marksmanship you can use a simple bow and a light crossbow, the simplest of the ranged weapons. Then as Marksmanship increases your damage with both bows and crossbows increases. Maybe at 90 or 100 you naturally have a slightly longer range with all ranged weapons. This skill signifies your basic knowledge of ranged weapons and an increasing general knowledge of things like how wind will effect your shot, what angle you'll need to fire at to get the best trajectory to your target, etc. Maybe at most it also dictates when you can use the more specialist kinds of ammunition. It then branches to Crossbows and Bows. At 0 of each you get to use the Short Bow or the Arbalest as recognition of your specializing in one weapon over the other. Otherwise these trees can remain the same, it makes sense that as you master one weapon you would get faster with it and learn special trickshots.
Barring this...maybe just merge the two trees into Marksmanship. I realize it ruins the realism by allowing me to power myself up to 100 using a bow and then turn around and suddenly be super proficient with a crossbow that I've never held once, but in contrast there are plenty of other not "real" elements to this game as well. I know everyone's fun is different, but shouldn't fun come before real most of the time at least?