Ok that's a lot of info, thanks.
I didn't had full draw at level 8, nor explo shot, I went for more defensive build (picking the roll from subterfuge for both me and Sera, as well as fade step for Solas, so I can instantly reposition all 3 ranged), I also went for leaping shot instead of Explosive (Sera will be tempest of course, and myself either Assassin or Tempest for this playthrough, of course will make a save backup before picking specialization so I can try artificer with Varric and prolly Cole on next one from skyhold).
Point is, 93 dps crafted spiked bows, I hit from max range ~500-800 damage with long shot, depending on target armor (~500 on 2h guys / grizzly bears, 600 on footmen, 700-800 on archers). Stealth seems to be bugged, I don't notice the 50% bonus damage at all (AI disabled, both me and sera stealthing and opening with long shots on same archer level 8, 2.270 hp, with elevation, same damage as if we are on even ground without stealth.....).
The problem with knocking down targets is that you can't really shoot them most of the time until they get back up because of line of sight problems (you can't always initiate fights and setup, sometimes you just wander through an area and mobs spawn on top of you etc, or terrain doesn't allow for much positioning due to LoS restrictions).
How is dex affected by DR? I thought it's a great stat to pump for the critical damage bonus as well as the attack bonus. Sure cunning is nice, but after 45% crit chance am not sure it will benefit as much (non artificer) to damage output than critical damage.
Ok so Full Draw OHK an archer. Then what? Fight scenario in hinterlands vs bandits: 2 x 2h dudes, 5k+ HP, 2 x archers, 2 x prowlers (possibly 3 mabari to add depending from what angle you approach the camp, and if you find / kill them before). You can remove 2 archers or 1 prowler in your initiation, then fight is on, you have a tank that needs to grab 2 x 2h dudes attention and manually position when they pop Guard and do the AoE thingie, as well as the prowler(s), if a prowler gets to Solas / Sera they are as good as dead or will eat potions like no tomorrow until you can kill them (due to their stealth, which happens very often on NM for me, they hit once or twice, then circle you in stealth, if you focus on popping them from stealth with manual shooting stuff, then you can't give orders to your tank etc).
I know how to deal with the mobs, the problem is I can't see realistically how you are doing so much damage to take them out fast at that level, while also not taking any significant damage yourself, due to severe lack of CC.
Or the quest to get 3 greater bear claws, when you are guaranteed to get 2 of those bears at once, possibly a normal brown one too, and either 3 mabari or 2 prowlers will happily join in every single time.
As Matth85 said, sure you can get to a point where Cas only takes 1 dmg from front, but: 2 bears doing the Stand Up smash move + 2 prowlers / 3 mabari which most likely won't attack her from the front angle, even if you manually pilot your tank, you can't dodge / block everything, a single knockdown or prowler ambush from behind and she will lose all guard and get hurt bad.
On the other side, in my previous playthrough, mage PC with Vivienne, Sera and Cas, I had no such problems due to more CC available early on and double barriers. Sure damage output was lower, but survival was greatly increased, access to more magic damage that ignores armor etc.