With just 3 points spent in crafting (1 point if you get the Pragmatic trait), and a few +crafting items which are fairly common throughout the course of the game, you can easily craft all the arrows you need. There are multiple places where recipes are listed. Any Ranger build can spare 1-3 points in order to have (by end game) any special arrow you want. Or put it on another character or a henchman. Early game you can make (at least) stunning and poison arrows very easily, and probably more that I'm forgetting. So yeah, Rangers have probably the MOST utility and access to damage types in the game, limited only by how many arrows you buy/find/craft. I've definitely relied on my Ranger as a crutch in a few hard fights on Hard.
The rogue, you're right it does require some setup, but NO WAY does a warrior match the DPS of backstab daggers. You can backstab 2-3 times for each swing a 2h warrior makes. With a few mobility skills, for example take the ranger one and the rogue one, or have a mage feather drop you, you can instantly, turn 1 teleport to the back of the enemy ranks, then cloak or use invisibility. Turn 2 pick a mage or archer or other dangerous enemy and destroy them. The warrior can't do that (or I guess it could if you took rogue and ranger and invisibility skills and traits but then ... it's not really a warrior is it?).
I'm sure others can speak with even more knowledge as I'm pretty early in the game so far but I've definitely gotten great use out of my Dex based characters.