Disagree with the above. Archers, for example, are well balanced. If they want to be accurate, they have to be 100% dedicated to archery, which means they have at most 2 or 3 (i don't remember exactly) skill points to put into either athlethics or PS, which still doesn't make them either good kiters or actually viable in melee.
My solution would be to either up the str requirements of xbows, so as to reduce the maximum agility (and thus athlethics) that you can reach with it, at least without taking away skillpoints from PS, and/or drastically increasing the weight of xbows, to reduce their running speed.
Still, not a full solution, i guess, but probably the best we have without WSE.