You said "the brake never stops the prop entirely". Do you mean the brake stops the prop and it spins up from airflow, or it really does not stop the prop?
The latter, it brakes strongly (in under 2 sec) but leaves the prop turning v e r y slow, ~3 r p sec.
After timer cuts out, I do my 'dive to level' from ~45deg to hit level right in front of the judges and having sufficient speed to glide a full lap till touchdown. Wouldn't be possible without a brake. Then somewhere during that lap the prop comes to a standstill.
I found that Bob's Genesis (without a brake) suffered a lot less from the spinning prop than the Blue Pearl (the WCh/Test plane Henk de Jong and I converted) Under power both planes were eerily similar in feel.
The brake on a CC ESC can bring the prop to a stop if that is the case.
But you weren't using governor, were you?
For some reason I remember the brake stopping my prop entirely (and the prop didn't spin up from airflow). Maybe it is because I use less pitch than you? I think lower pitch props would be less likely to spin from airflow. It may also be possible that my motor has more cogging effect than yours. I believe you are using Plettenberg also, so that may not be the case either. (I could be mistaken, it's been a few months since I have flown).
I fly a AXI 2826-10 with a Graupner 12x6 el. prop. Like said I'm using 6" and I even tend to go to more pitch and less revs to load the governor more.
We found we had a 400->800 Watt kick when suddenly loading the prop. The CC took it without blinking, the Kontronik (you could hear the revs drop for a split second) really lagged so much that it never could cope with a good corner, hence the need for kicking up revs with 2 % before the square eights.... Maybe the brake also suffers from this 'safety' that heli's might need. Or is it to prevent claims from dumb***ses that keep stripping the gears on their choppers?
What I need apparently, is new software for my CC-45 to make the brake combine with governor.... But they wouldn't do that for me last year when I asked
So that's why I changed to Kontronik...