The only reason some people may consider Kridershot BIS is that the sentries will also fire your generator, i.e. Elemental Arrow. Now, Elemental Arrow of course does much more dmg. than any other generator, yet, it never reaches the dmg. of the Rocket skills or even LfB (for group play only). The fact is, the dmg. per hatred is still much higher and efficient if you use an ancient 2h xbow. I also used to think that kridershot is BIS, yet, once your realize one thing, Kridershot becomes redundant:
For High lvl. play, there is no need for a generator skill at all.
I play Grift solo 44 (top 50 seasonal European ladder) and use an ancient arcane barb. Other than some, I don't use any generator primary, but only rely on Health globes (wraps), punishment and seeth or MfD - ME for generation. This allows me to basically use CA at least 1 every 3 sec (for taeguk in GR) and clear without having to worry about a primary.
In the end, Kridershot is not BIS, the leaderboards on the PTR and the current new shifts reaffirm this. The dmg. you get out of your CA (or MS if you feel like it) is paramount, thus an ancient Arcane Barb, Etrayu or Calamity is what you want to look for if you really want to max out your potential in GR.
It's too early to make such a statement. The vast majority of us haven't set a foot online or in a "competitive spirited" greater rift in months. The season unofficially ended before ancient items came around.
Wait until the season begins for real before making your final judgment, although, I do agree with your reasoning.
Use Archery for the 8% damage buff. With the max reroll you have a pretty hard hitting weapon. 2H X-bows still have the advantage of a narrower Damage Range. But with the passive, your damage base will hit harder. Try it. My non-anchient is getting over 30% higher crits.