This technique is explicitly frowned upon in a number of licensing tests. Hand is required to be completely on throttle, or all four fingers completely on brake. So I'm not sure "completely irresponsible" is the right term, as it's actually taught that way.
If you drop the throttle, you will already begin to decelerate from the engine your fingers are A LOT faster than "a second or two" in clasping the brake... easily sub one second.
Might be frowned upon, but it saved my life a few times.
If you drop throttle on a belt or variator transmission.. well the belt slips.
On a typical say japanese 600-ish cc with chain final drive, dropping throttle would not do 1/5 of what pulling the front brake will do.
If you have an emergency braking situation the rear brake is not only useless, it's a hazard, the rear wheel just lifts and loses traction and if you lock the rear wheel, not only you lose gyro stab effect, when you release front brakes what happens is that you highside. (crash that is).
Rear brake is for parking or slow coasting.
They all are really out there to kill you, so you must be ready at all times.
Not to mention that the rear brake comes into play as applying the rear brake will transfer weight to the front allowing you to apply your front brakes harder.
Not in my experience (20yrs). If it's all-in-or-we're dead, you either do a stoppie and hope, or do a deliberate lowside and also hope someone will patch you up once they dislodge your parts from wherever you end up in.
In either case it's front brake. A bit of tilt for the second case. The rear brake is not needed at all.
If it's just a overspeed corner, you try to slow down gently, while maintaining both wheels on the trajectory. So just a little play with throttle and just a little front brake so that the bike stays balanced so to say. No rear brake at all because dropping the throttle a bit is all that's needed for the rear wheel.
If that is not enough, you're not going to make that corner, you have had too much speed coming in, and you will pay for that right now by crashing into something.
I learned this in 1990s when I first started riding.
If you drop the throttle, you will already begin to decelerate from the engine your fingers are A LOT faster than "a second or two" in clasping the brake... easily sub one second.