Hall's Olympic Trials race was incredible, but it also proves the point. While he was on fire that day, he didn't need to go that fast. I suspect Rupp would have treated that race as business-as-usual, locked up the victory, and saved his "going to the well" for when it really matters.
This is total hindsight rationalization. Ritz's second place time in 2008 was faster than Rupp's winning time in 2016. Hall had to go fast. He was racing a loaded field in 2008 -- literally no one thought he was anything other than genius on that day.
Also, Hall's next race was a 2:06 for 5th place in London, so I'm pretty sure that 2:09 wasn't him "going to the well".
Look, I think Rupp's the greatest US distance runner ever, and totally appreciate the idea that he could come up big against Hall if it mattered. But Hall's marathon resume is far, far superior to Rupp's (he broke 2:08:40 five times -- twice in his first three marathons!), and Rupp has won exactly one race of note. If Hall was the better marathoner at his peak, I think he beats Rupp 6 or 7 out of 10 times.