Energy loss equals drag times distance covered. You will have less energy (i e lower airspeed) at point B if you pitched down to increase speed. If you instead only levelled off to the initial airspeed and then descended at this airspeed, you'd be lower at point B using the second method.
Every glider pilot is well aware of this. If you are way high, pop the boards and dive for the ground.
I don't really want to have an argument.
Getting gear and flaps and speedbrakes out beats the drag of speedbrakes plus drag increase from higher speed. Every glider pilot does not have the huge amount of form drag that you can introduce on an airliner.
But you may well be right. I just found that inside the TMA, slow and dirty works better than fast, clean and decell.
It has the added advantage of not stressing to make the slot.