I think you whacked the nail on the head there, good post. I think BRS have played their cards well, albeit with the mediocre set they were handed, to produce an airport which has a solid collection of year-round destinations and decent passenger numbers.
In an ideal world "Bristol Airport" would be at Filton, with it's pre-existing rail link and it's own junction off the M5.. but as you infer, that ship sailed a long time ago. However, as ever a long runway doesn't mean prosperity and I think BRS would struggle with LHR just up the road.. or indeed just up the motorway had FZO been developed. But c'est la vie.