IIRC it's easy as pie
Altair -> defensive skills (except when he's alone against multiple Orc enemies)
Styx -> offensive skills (that skill that boosts his critical chance upgraded with +50% dodge is game breaking especially combined with multi-dagger skill)
I hear you, I stared getting the hang if it but still found I had split my points too evenly between attack and defense so I wasn't effective in either. This became apparent in certain fights, like against the Shaman. I was about 10 hours into the game. Also every level seemed the same from a gameplay perspective. A linear path from A to B with the same types of monsters just in different size groups...goblin, dogs or humans . I may install it again, but I doubt it
I agree level design and stealth mechanics are... rudimentary, but one needs to take into account this game was developed on a shoestring budget (even compared to Game of Thrones from same developer), still setting, combat and characters ultimately were good enough to make the game worth buying on release. I really would not mind a sequel.