Hm, it's still a bit strange. I have crossbow on something around 30 and tried a sniper crossbow once. With weapon Mastery 2 I got +2 every second shot or so. Would that be even higher if I had WM 10?
I usually never increase it more than up to 2. Everything else comes from fighting, and on level 32 I have bows and 2h weapons about 300, 1h and throwing weapons about 160 (as I used throwing daggers before and sometimes use the bastard sword 1h). And if someone tells me that he has the skill at 400 or even more, It just doesn't matter to me. Why use valuable skillpoints if it only gives you peanuts of advantages? Sure, with AGI 30 it would look cooler to have WM at 10, but I just don't have the points. And if I would, I'd invest them in other skills.
I use a Bastard Sword 2h as my main weapon (PS 6) and a Short Bow (PD 1) as secondary weapon. With all relevant STR-skills on 6 (my maximum) and athletics, riding and shield on 10/9/8 I see absolutely no point in increasing WM. And yes, riding really increases speed and maneuver. If you once have riding that high, you'll miss it if your way of playing is based on outmaneuvering enemies but your char has a low riding skill (try it out with cheating by editing the exported char file). As mentioned the horse is the only option to survive larger battles, although I managed to fight and kill 8 Dark Knights/Hunters with my first char (AGI-based archer on foot with a Sword of War as secondary weapon). But that is only possible with really good terrain and some luck (you have to keep as many of them as possible in sight or at least know which ones are close to you and from where they come).
I don't do the highest damage, compared with true 2h users, but I'm much more flexible. A speedy shield against ranged troops (that's why I need the shield skill, a big shield just looks awful with my char

, and these crossbowmen can be a pain in the ass), the 2h version of the sword for melee, and the bow for far distances or riders that survived my first strike and try to run away (shoot the horse, kill the guy). High riding to completely outmaneuver large numbers of mounted troops (especially lancers). With this kind of playing it's absolutely useless to invest more points to WM, since it doesn't matter if I do 5 dmg more or less. I have speed through AGI and damage through Power Strike, and if I see it right that gives alot more advantage than Weapon Mastery. Plus if you really want to have something like an advantage through WM, you'll have to train it at the very beginning. Increasing it at level 30 would be meaningless, since you already have high proficiencies.
EDIT: Again too much text. I have to work on that...
