Nope not forgetting that at all - I'm simply saying that the aerodynamic penalty is small at high yaw angles, I've seen the figure of 4 watts bandied about, and it's negligible/no penalty present at low yaw angles. In the context of deciding between a disc and rim brake model, aerodynamics of the braking system shouldn't even be a consideration in my opinion. There are other differences and compromises to be made that would affect the decision making process before you start splitting hairs on aerodynamics.
Losing 4 watts in the small context of high yaw angles (which FLO aptly shows is a minimal percentage of ride time) doesn't strike me a massive issue compared to what discs bring to the table in other situations. 4 watts when you're chasing a split in a cross wind isn't going to be the deciding factor of you making it across or not.
Of course this point relies on being able to use them racing - which unless you live in the U.S shouldn't factor into the discussion just yet.
Maybe 4 watts compared to standard brakes, but it would be more when compared to the hidden brakes like you find on many aero bikes. I'd say that when you are in the gutter fighting to hang on that 4+ watts could absolutely be the difference between hanging on or getting dropped. I'm typically talking handicap races here when scratch or block catch your group, there is a crosswind and they put it into the gutter. If you can hang until the road changes direction there is a good chance of figuring in the prize money. It doesn't matter that this occurrence is for just a small percentage of the ride as it is the critical time that decides the race outcome. I have seen this happen time, after time after time.
Races in Australia are pretty much devoid of descents so disc brakes bring additional aerodynamic drag and weight to the table without realising any of their braking benefits.
Still going to respectfully disagree that 4 watts is going to be the difference in that situation. You might get dropped but it's not because you couldn't put out 4 more watts. Adding 4 extra watts to your output would increase your speed by such a minimal amount it's simply not going to matter in this situation. At race speeds of 35kmh an increase of 20 watts would get you to roughly 35.5kmh, so how much does 4 watts get you? Good race craft of following the move and position will matter more in this situation, not your braking system.
Just because it's a cross wind also doesn't necessarily mean it's a high yaw angle either, it's influenced by speed and if you are drafting. There is some great info on SlowTwitch about yaw angles if you want to check it out further.
As for gaining the benefits of discs I guess it depends on where you race in Australia and what races you enter. I would love discs for some Crit courses, being able to brake later into a corner and potentially carry more speed because of the finer control would outweigh the small aerodynamic penalty. All else being equal of course. I would also love to use them in wet races as well. My local races here in QLD are quite hilly too.
Funny thing is that as we are in Australia and we can't use them in races so there should be other more pressing reasons for choosing between disc or rim brakes than how they will affect your racing.