Q: “What is your opinion on the frequently expressed dictum “trail brake until apex then back on throttle starting at the apex”?”
A: My opinion is that this dictum is total crap! About the only thing that I know of in performance and race driving that follows a “always do this” dictum is that there is nothing that always works! If someone tells you to always do something, run away and ignore what they just said. There are just about as many exceptions to messages like this as there are times when they work.
There are corners where you should release the brakes at the turn-in point, and therefore not trail brake at all; there are corners where you should trail brake far into the corner. There are corners where you should begin applying the throttle before the apex; there are corners where you should begin applying the throttle after the apex. And everything in between.
All of this depends on how well your car turns in, whether you’re focusing on exit speed more than entry, and track conditions.
I’ll also say that I have a hard time thinking of a corner where I’d want to trail brake all the way to the apex – and I’m a big proponent of the use of trail braking. The EoB (End-of-Braking, where you finish braking) is typically somewhere between the turn-in point and apex, but if you’re just finishing trail braking at the apex, I suspect your entry speed was too high and you’re in a bit of a “save it” mode.