If you are already at QS2, this might be a bit late for advice, but imo:
Archer:
-I’d change to Oblique 4 and Full Draw 1. Extra utility at the cost of minimal damage, especially for PVP.
QS:
-Forget Rapid Fire, it’s not good at Level 10 it won’t be good at level 5. Drop it to 1 for the Attribute.
-No reason to put more than one point in Stone Picking. Yes it makes life easier, but life would be even easier than that if you just picked up your stones in advance and never had to worry about it.
-Put those extra 6 points into Pavise because…well…there is no where else to put them, and more hits/duration will be more useful than any other skill you could put them in.
Scout:
-You could consider dropping a skill to 4 to get FluFlu 1. I have no idea if it works on players, but at least in PVE the utility of the skill isn’t bad.
Rogue:
-Vendetta 0. Not worth it. Never worth it.
-I’d use those points to get Sneak Hit 10, for full uptime (and more crit rate).
-Leftover points I’d throw in Lacrymator for the duration.
As far as Rank 8, from what I’ve seen all Mergen skills require a 2h bow. Hackapelle honestly seems like it was almost entirely designed to work with Rogue though.
The only Rogue skill that needs a dagger is Backstab, so you could easily just throw a dagger into your secondary weapon slot and let the autoswitch take care of it.
Meanwhile what does Hackapelle offer?
-Added mobility from mount for general purposes and getting Back hits.
-Storm Bolt x Back Stab combo for your heavy bleeding
-The ability to use one handed swords in off-hand to get a large damage boost
Admittedly, it’s not much. On the other hand, Mergen seems to add little more than damage, which is not terrible as the only damage skill Rogue’s really get across all three ranks is Back Stab. If you don’t mind switching out to use a 2h bow (and just autoswitching for back stab), Mergen might fill in some of the holes that the Rogue class has in general. The main problem I’d see with Mergen is that you can’t use Stone Shot with a 2h Bow, and Stone Shot seems like a very important skill to not be able to use. Autoswitch might take care of that, but if you get the FPS stutter from weapon switching, that will be a big problem.
I personally think Hackapelle has more to offer, but I don’t know enough about Mergen to rule it out. Those are my thoughts on the matter though.