Rangers are more than viable without any scoundrel abilities.
They need perception anyway, so my first intended ranger/scoundrel hybrid ended as a pure ranger in gameplay with 15 perception (4 from gear) at level 21. Had 15 opening action points since level 17 and was the first to move in any fight, allowing for a minimum of 3 special shots at fight start. Nice combos like 3 static cloud arrows or 2 poison cloud arrows followed by an explosive etc. Special arrows against abilities and resistances for boss fights.
Despite 2 mages as glass cannons I beleive the ranger had the highest skill core from all 4 characters.
So yes - rangers are viable, although youエll find quite some threads on gamesfaq or steam doubting that, but these come from guys who donエt know the game.
Regards,
Thorsten