FFS going down the box shifting from top or even 5th down through the box to 2nd without releaseing the clutch sounds like a disaster waiting to happen. Assuming 5th gear at say 60 mph, throttle shut, down through the box to 2nd gear with no revs, it sounds like back wheel lock up time to me, not ideal on the straight let alone entering a bend.
I think I will stick to the multiple blip and use each gears braking effect, not only is it effective braking it is also smooth and progressive, plus you in the right gear with back wheel under control ready to power out of the bend.
There are not that many bends on the average ride or commute that requires dropping from top to second gear to take the bend, if we are talking about braking in an emergency I certainly would not be thinking about how many gears I have dropped through before dropping the clutch.
The old saying is in that situation look where you want to go not look at what you are trying to miss, avoidance tactics in that situation are often more productive than slamming those big twin disk and 4 pot callipers on and stomping on the back brake resulting a rear ending lock up.
A lot of bike disasters (not all) are caused by the rider losing his or her bottle.I know cos I done it, felt I have over cooked it approaching a corner braked causeing the bike to try to stand up at that point realising that I'm not going to make it round the bend so in panic stand on the brakes, it always ends in tears.
The best rider manuals will tell you right gear right time the instant power available to you can get you out of trouble. 60 mph clutch disengaged in second gear ain't no use to anyone.