I think there is a big difference between types of crossbows that were used back in the day.
I doubt the crossbow a wizard would pick up would have a very high draw weight and therefore being pretty weak seems realistic to me.
I don't think the crossbows we use in DDO represent any kind of wench, windlass or rack and pinion type crossbow with a mechanical advantage to compensate for poor strength.
I envision the light and heavy crossbows as simple hand operated machines, so having the base damage be similar to a bow but the rate of fire much less seems realistic to me.
The great crossbow seems like a a siege crossbow or a gastraphetes and should be slow as molasses. You don't really carry these things as a personal to-go arm.
The repeating crossbow is clearly trying to be a a cho-ku-nu, what with the top loading magazine, and by all rights should have less base damage and less range but for the purposes of the game is beefed up uber to make taking the feat worth it.
I'm fine with the way these are used in the game and see no reason to change anything too much.
If people want crossbow feats that would be fine but make me scratch my head as to why you would choose a crossbow to spend feats on rather than a bow that ultimately, after mastering, would be more deadly in the game as it is in real life.