Backstab and Guerilla are both too important to Scoundrel damage output. I'd recommend removing Backstab entirely and just make daggers do extra damage when attacking from a flank.
As for Marksman, Quickdraw is the one I think should be made standard. Almost no respectable Marksman build would go without it, so it reduces your freedom in talent choice.
Neither Mage or Warrior have talents as necessary for their damage. Bully is the closest thing for warriors, but it applies to Scoundrel and Marksmen as well.
Then there's the long list of total dud talents:
http://divinity.gamepedia.com/Talents - if you're unfamiliar with some of them.
All skilled up: 2 is not enough considering we get near 50 ability points from leveling, but only 7 talents.
- Also consider swapping the terms skills and abilities. Right now it's just confusing and this talent is a great example. Abilities should be the actual...abilities on our bars. Skills are how adept we are with different types of abilities.
Anaconda: Just not enough damage boost to what's already a lackluster weapon options - 2h is just outright better currently
Arrow Recovery: Pathetic. 20% is nothing, and arrows are easy enough to come by. If anything, this should be @ 100% for people who want to skip the crafting micromanagement that comes with playing Marksman.
Know it All/Bigger and Better: Attributes are more limited than abilities, but this is still of questionable value when we've got more dramatic boosts to choose from.
Courageous: This is pure awful, you can get a trait that makes it entirely obsolete without getting the downside, and fear isn't common enough to worry that much about it either.
Demon/Ice King: The situational and low % proc benefits are dramatically outweighed by the permanent downsides.
Elemental Affinity/Elemental Ranger: Way too situational.
Escapist: Why be better at fighting when you can be better at running away? Well...probably because you can already easily escape most battles without this talent. Complete waste.
Five-Star Diner: Food for the most part isn't worth using currently.
Light Stepper: Almost no reason to get this over Bigger and Better to get an actual point in Perception. Just not good at all.
Morning Person: This talent pretty much depends on you failing dramatically, which you're more likely to do with one less good talent(when you've taken this one, for example)
My Precious: I can't think of a redeeming quality to this, utterly useless.
Packmule: See above.
Politician: Losing an attribute for a gain to an ability is pretty awful considering how many of each you get(way more abilities than attributes). And charisma isn't even a very worthwhile ability.
Scientist: Well, it's better than the above, but still bad for the same reason that abilties are too abundant to justify spending talents on.
Sidestep/Sidewinder: Just not substantial enough defensive talents.
Stench: This relies on your failure to use smart positioning and/or control skills.
Walk it Off: Positive buffs are a big deal while you can build up resistances to most negative effects or avoid them. One turn less of absorb elements, fortify, wildfire, etc. etc. makes this talent kind of a net negative.
What a Rush: Far too situational and dependent on you being low health which you generally want to avoid or amend quickly. This'd be better if you simply got extra AP from taking damage.