You don't get much advantage if darts hits grounded. It looks like either -/+0 or a few +. Then again maybe I'm an idiot.
Darts give about +9-10 frames on hit imo. Not fast enough for 2K being guaranteed, but fast enough to 2K beat Lei's early frames of cry baby (i6).
About CH fc A+B 6A+B it's a nice find.
I checked half of the cast and it doesn't connect on:
mitsu, zwei, asta, voldo, cervy, nighty, yoshi, alpha.
and connects on:
pata, lei, natsu, pyrra, opra, ivy, maxi (mostly), algol.
The differences are in falling animations. Mitsu, zwei, yoshi etc. are falling on their right side and then it wont connect (of course from different angle it can connect).
But still we can make 3B with usually connects, or 6B with always connects on them and put them on the BT state where your another 6B will be escapable only on one side, your A+B cant be interrupted (on Alpha your A+B will even put him again on BT state lol).
3KKK also works but not always ant not on all.
The second group (pata, lei...) fall on their left side and 6A+B always connects, so no problem here.