It was my understanding Pandora, that if there is any likelyhood of using Reserve fuel, one must at the very least make a PAN call. That would have provided the necessary paperwork (ASR cc:BALPA) for someone impartial to judge the individuals actions.
I have been in your situation MANY times as an FO on a S/H fleet at LHR. I tend to be a bit wary when TSRA is written on any TAF due to the circumstances that led to Britannia crashing at Gerona a few years back, but this waryness has fallen on deaf ears a few times in my career. So many times that I never take the "I think we'll use SWORD/Flight Plan fuel" response to heart. I would gladly enjoy the challenge of diverting to MXP when LIN is 800m in +RA and having to make a MAYDAY call because MXP ask us to join the hold. That would in my opinion make the individual who ignored my plea for 'an extra half hour' take it in future.
Why do these OLD + BOLD min fuel characters exist?
It is my belief that they use their experience of operating in airspace that 10 years ago had half the aircraft operating in it and apply that to their own 'personal' risk analysis. Your more sceptical analysis does not stand up to his 'experience', despite the fact that it indeed may be more accurate.