Having a laugh at seasoned travelers telling other season travelers when to show up at the airport. Big difference between LHR & LNK and I think most would know that.
I don't go to MRY until 10 min after the plane has taken off from LA and that gives me enough time. Could I have shown up as the OP did? Of course but that's just too close for my own personal comfort. Could someone with checked bags walk through the door of the airport and be at the gate in less than 5 minutes? Absolutely.
The GA was wrong. FT blaming the OP is wrong.