Twiglet1: Been there, done that. You illustrate exactly a point I've been thumping on for years; the XAA's bent the rules to suit the performance of the a/c and the routes flown. They came up with 'fixes' to allow the bends to be applied. Later on there was the 'Florida dispensation'. B767 could do it direct, non-stop, but it was a long duty. The return was also long, after <24hrs rest. To avoid having extra nights of layover you could opt for a 24hr turn-round and an extra day off at home base. I never understood how extra rest AFTER the event made the event any safer or more acceptable. Having said that, for me a 1 day lay-over was less tiring than 2. To be truly fresh I needed 3 days to recover the jet-lag from the outbound; but it's personal.
But I still believe it is the case that FL's have evolved not via good medical common sense but via a/c performance and lack of coordinated crew opposition.