Dude, people never see stuff coming after 6C because there's never anything to do afterwards, once Noels start doing it, people are gonna start expecting it, at that point it's just gonna be an unsafe gimmick. 5A and 6C work ALMOST the same way for your "mixup" but lets break it down real quick:
Options after a delay 6C:
2C (Low)
Grab (Throw)
6B (Overhead)
Second Hit (Oops)
Options after a delay 5A:
2C (Low)
Grab (Throw)
6B (Overhead)
2B (Low)
2A (Now I'm +1 suck on it)
Jump Cancel (I'm out of here, or maybe I'm jumping in)
5B (Will catch jump outs)
and then my personal favorite:
STAGGERS ALL DAY
Obviously if you do nothing but 5A > 6B every time, people are gonna mash out eventually, but if you know how to frame trap after 5A, which is painfully easy to do, then you'll start scaring people who mash, which will allow you to do 5A > 6B again, or a tick throw. My point is that 6C as a blockstring starter is just a gimmick, while Noel's standard options up close are more solid, hell if her 6B had frame advantage then Noel would be TOO good up close, especially now since she has Hell's Fang :P
Still gonna miss 6B > 6C though.