@Raban
In a nutshell, bows just do way more damage than xbow due to the nature of the bow specialisation vs xbow specialisation. The crit component of Xbow doesn't work with Marksman skills nor with special arrows, whereas those skills and those special arrows have high priority because they do very high damage per AP spent. And it only gets worse as you progress in the game, because you learn more and stronger skills (which make you use less auto attack overall in proportion), and because you progess farther and farther in the bow specialisation.
Best crafted Xbow only do 110% the damage of crafted bow, for 125% of the AP cost. And the bow specialisation work for skill (150% damage), whereas the Xbow specialisation doesn't. So, as far as skills and special arrows are concerned, bows end up doing 36% more damage than xbows (150%/110%). The "Ricochet" skill also cost 5 AP for Xbows and only 4 for bows, but I discounted that.
In the case of auto attacks, and with 50% crossbow crit engame (25% for 5 in spec, 10% from the weapon itself, and 15% from trait and perception and buff), if we assume similar damage per AP for bows and Xbows (which isn't the case), bows do overall 150% * 115% damage (bow specialisation bonus + crit bonus), whereas Xbows do 100% * 200% (xbow spec affects critical damage). That would be 16% more damage from Xbows auto attacks. If you factor in the non equivalent damage per AP (only 110% damage for 125% AP), it becomes
150% * 115% vs (110% / 125%) * 100% * 200%
which is only a 2% bonus.
All this being said, the marksman is the best class in the game, and the game isn't hard enough not to be beaten easily even with an Xbow marksman. So I wouldn't advice against building an Xbow marksman if such is your fantasy. But building an Xbow marksman because you think it's optimized is just misguided. Otherwise, there's plenty of good advice to optimize the fun out of an Xbow marksman (guerilla build).
