Virtuosus, you don't understand how damage works in this game. A bow's base damage isn't simply added onto arrow damage. It's multiplied by several variables such as your archery level and overdraw perks. The arrow damage then gets added on top, which is why arrow damage isn't very significant.
As an example, at 100 archery with max overdraw, a 5 point difference in base damage will result in a 15 total damage difference.
Furthermore, you claim that crossbow reloading leaves the player defenseless. How is that any different from being defenseless while you're nocking + drawing a bow? You can run at full speed while reloading the crossbow.
I know how damage works in this game. Sneak attacking would make the damage difference a bit larger as well, as would Fortify Archery enchantments. I still don't see how such a small amount of damage can be considered overpowered? Crossbow maximum damage can get higher than a bow, so what? They also take longer to reload, and as I said, they have their drawbacks.
You can NOT "run at full speed while reloading the crossbow." Have you ever tried using the crossbow at all, or are you just basing your assumptions off what other people say?

Besides, there's another difference between knocking an arrow and reloading a crossbow. You can choose to knock an arrow whenever you want, but the game forces you to reload your crossbow immediately after taking a shot. The only way to avoid it is to spam the X button as soon as your shot goes off to sheathe your crossbow, and even that isn't foolproof as it doesn't always work. If you don't use this trick to immediately put away your crossbow after a shot, you're forced into the reloading animation, where you're left wide open for attacks from enemies, which can mean immediate death depending on how squishy you are at high difficulties. The worst part is, when you're reloading, your movement speed is decreased by a large amount, meaning you cannot dodge incoming attacks while reloading unless you're perked. (Much like the bow when knocking an arrow, except reloading your crossbow is forced.) Also, if you knock an arrow with your bow you can simply press X to put the arrow away, but if you're reloading a crossbow, pressing X doesn't cancel the reload animation, you just continue to do it.
I wonder how much some of you have actually used the crossbow for, honestly. I use both the bow and crossbow for different character archetypes, and my Thief character actually uses both for different situations, and both have advantages and disadvantages and I'd say they're quite balanced well and nowhere near "overpowered." If anything, the fault lies at the game being too easy, and crafting skills are to blame because they are simply overpowered, not crossbows.