Power Disc Brakes not working on hard stop?

If you brought it to me, the first thing I'd do is take it for a test drive and verify the pedal has limited travel.
I may check for air, but you said bled .
The next thing I'd do is set the emergency to drag while driving.
This moves the shoes into contact with drums to remove any travel to get the shoes to apply. Now ANY hydraulic movement by the m/c should have an immediate result somewhere, fr/back, if not, find out why.
Next drive it, and I would expect the pedal to be "higher", right there, and braking to be improved.
If no difference, as mentioned, open bleeders, press pedal, it should go to floor or vastly farther than now.
If it won't go to floor, find out why, cuz that's why your pedal hits a "board".
If that doesn't give an improvement -
The other thing I would try, is plug the m/c exit ports with no air in the master, expecting that the pedal should be rock hard at the very top, with no travel, if there is travel, find out where.

The booster travel may not be sufficient.
To plug ports, I have nipped off the head of a drywall/shingle nail to be like thumbtack, trim head to fit m/c outlet port, quickly undo outlet tubes, slip the tack into tube and re-tighten tube into m/c, effectively plugging outlets.
Mann , as always, good luck .