Adelheid

After reading that I immediately went to test, having thought I'd done it at least a few times in the past... I actually couldn't forward dash after JIing with that exact string, but using f.S instead of HS, I succeeded once... I kept screwing up my timing after that and couldn't reproduce it (probably because I typically play on the stick, but had to do the tests on a pad as my stick doesn't have a functional down right now), though, but still, it definitely can be done when not in neutral.

Is it really that worthwhile doing that rather than just doing bomber loops? Granted, you need to be somewhat close to the corner, but if you really need more space you can always just add an FB bomber... The only time it's really not going to work is when it's close to the wrong corner, in my experience. This is useful in that case, but really, I've never had the case where dusting was convenient that I couldn't just transition to bomber loops with the standard impossible dust.

There is no proration on them. The reason the combo deals less damage overall when all of them hit is because each hit lowers the opponent's guard bar a bit (By about 3 points each, IIRC - The guard bar has 257 units to it, going from -128 to 128.). As long as the guard bar is below 0 (the midpoint), the lower the opponent's guard bar, the less damage they take, so since each hit of Rensen doesn't do much damage (20 each, without any damage scaling), hitting with every hit will mean you do a bit less damage in your combos, since everything after the Rensen will deal a bit less damage hitting with 3 hits than hitting with 2. Note that this doesn't apply if the opponent's guard bar has been jacked up, since as long as the guard bar is 0 or higher it won't scale damage - in that case, more hits = more damage.

This honestly seems like an incredibly unwieldly motion. I do 6923.

That sounds like a personal problem.

If they've seen it once, they'll never fall for it again. Trust me on this one

Raiei isn't a very fast move. With 28 frames of startup, cancelling it from a move like 2P which is only level 2 gives them more than enough time to jump and throw you out of it if they're watching for it, unfortunately.