Rubik. I take it you're no pilot, though you're pretty good at flying to conclusions.
Who told you it was the pilot that "got his sums wrong"? Not even the daily hate published that gem of misinformation. He probably wanted about 6T. He couldn't possibly have made an error on that scale. 16T is more than he'd ever have carried in his career. Almost certainly a dozy refueller (and no one monitoring the refuel on the flight drck, admittedly).
Sadly the idiots who behaved in the way you proposed were the ones who really precipitated this
PR disaster.
I don't think defuelling is possible anywhere in the UK. Airports just don't have the equipment for it, and when it is done the fuel cannot be used as it is presumed contaminated and is effectively scrap.
Thus the aircraft has to be lightened another way. Hugely embarassing, but feel free to suggest a better way to do it, because your wisdom would be of great use to airlines hitherto constrained by Newtonian physics. You'd get a Nobel for it too.
The pilot was only the messenger, he didn't make the decision, the Operations manager did. The poor pilot had to communicate it, one of the worst situations imaginable.
How else do you decide who to offload apart from last ones to check in? Which is less contentious, offloading another 20 pax or the bags? And do you tell the frogs before, or after you've drained the swamp? Someone has to make all those decisions on the other end of a phone a hundred miles away. He can't please everyone. That bags decision is a very hard call.
Short of paying a decent overnight allowance and being very sympathetic in the face of no doubt endless furious abuse there's very little the airline can do but apologise. They can't achieve the impossible.
Its a pity though that the passengers haven't the wit to see that arguing and wailing that it's not fair can't change the situation. 37 had to get off eventually, and chosing to fight or argue just makes a difficult situation doubly unpleasant. If they refuse to walk off than maybe they have to be carried or
everyone is delayed there all day. But why screw everyone else up just because something doesn't suit
you? That is plain selfishness.
I have every sympathy with all the passengers except those who thought that confrontation would achieve anything but make a difficult situation far far worse.