Well it's true i most of the time die in close-medium range from thoses os xbows.
And as a "normal" pure archer, i have only 15 str and 0 IF, wich can explain this (and only 32 body armor).
Anyway, what i fear most from xbows is not their ability to take 1h/shield, but the "oh a guy with no shield, let's go 1m from him and shoot point blank, i can't miss for sure, ah ah ah".
But related to this topic : Leave the hunting and light xbow 1 slot, and the heavy and arbalest 2 slots. For the normal one, i really don't know. If you decide to put it on 2 slots, then add 3-6 bolts per... "boltquiver".