it might have been legal to fly from LAX to ALMOST London on three...but what about common sense?
keyword ALMOST London. they didn't make it.
Common sense: there's nothing else wrong with the aircraft, even if the aircraft loses another engine all terrain can be covered, there's countless alternate airports enroute if another engine fails, there's sufficient fuel on board to reach a decent airport enroute, it's an approved 'manoeuvre' by the manufacturer, company and safety regulator and, lastly, ALL the crew agree the same thing. There's plenty of common sense in all of that and just because your dyed-in-the-wool thinking won't allow you to think any more than Flap 30 doesn't mean the crew were mistaken in their actions nor worthy of your derisory comments.
No, they didn't make it to London but, guess what Einstein, they KNEW that was going to be the case before they were halfway across the US. Amazingly, even without your expert knowledge being available, they were able to figure out their course of action which ended up with a perfectly safe flight, less inconvenience for the pax and an easier repatriation of the machine. I know you hate anything across 'The Pond' but I reckon the the operator of the largest number of 747-400s in the world might have just an inkling as to what they're doing....even if asymmetric thrust was not part of the syllabus.