I tried it at an event and was slower too. Definitely hit ice mode and blew at least two braking points on seperate runs, immediately switched back.
With it in regular mode the car is more forgiving to stabbing the pedal for whatever reason, with diagnostic brake/pedal/dance mode the car will punish you for not being smooth on the brakes or just plain old freak out. ABS is still active in pedal/brake dance mode, it just seems to give way to ice mode much more readily. I'm not exactly in a position to go through and investigate like others around here.
http://www.sccaforums.com/forums/aft/392890
Try it at a Test and Tune event, a ideally with a skidpad so you can take the same two corners 20x in a row, make the change and then immediately do it another 20x times. When I did that it was a lightbulb, "Oh,
THAT'S trail braking!" because with the car in regular TC off mode it certainly tries it's best to keep you braking in a straight line.
To me it's a shift in how I brake, just because I CAN brake harder, doesn't mean I should, I really have to be more delicate in my braking application, I can't
stab at the brakes anymore, I have to
squeeze the pedal. I felt the weight transfer and effects of trail braking before in standard mode (part of that was really attacking the brakes), but there's so much more of it in diagnostic mode. I overdid it and lost the backend at least 3x during the first skidpad session with it off (to cut myself some slack and garner a bit of sympathy I was trying to figure out left foot braking at the same time), by the end of the day it felt like on demand rotation under braking.
It really is a 4th/5th mode in the traction control and changes how you step up to the limits of traction. Getting the most out of the car with TC on is very different than with TC off, and it's different again without EBD.
I balked at that too about a year ago, but didn't say anything (or maybe I did, it's probably in this thread) because academically speaking if what's going on here is correct, that's not a ridiculous statement.
It's definitely the case that EBD limits the trail braking potential of the 86 in standard modes. Effective and masterful use of the brake pedal is critical in being deemed a skilled driver, no argument can be made against that. Without using the trail braking available you're leaving speed on the table, plain and simple, that was established in racecars 40+ years ago by Jackie Stewart and Mark Donohue, earlier in motorbikes I believe, and it's the standard today. The best way to get faster is to raise your minimum speed in the corner, not brake later or accelerate harder.