I think it comes down to combo parts.
Ideally you want to have you best moves all up front. move A, move B, move C. But you can't necessarily do that based on hit stun, untechable time, etc.
The jigsaw puzzle comes together so that not being 6c first makes it easier to string things together. I still imagine the highest damage combos are going to come from 6c or 5c>6c, but people need to figure out how to fit them in.. Or maybe it won't.
Almost like how 623C is a critical part in Tsubaki's corner combos in CSEX, even tho the dmg/proration is really not that good? I dunno.
Similarly 6bb is looking like it is going to be a very important combo part in CP, the damage/proration are pretty decent, but more importantly, it's something else you can do the [4]6D>236D combo part off of.