In regards to fastpass backing up:
You don't notice until you've actually worked at an attraction with fastpass how much the line backs up with late arrivals.
Soarin' was the worst. People would show up 8 hours late and get in line after a parade, which would congest the queue. If the fastpass line was backed up, it would also bring the standby to a grinding halt.
It would be much better if Disney just started limiting the number of passes produced. Maybe increase the intervals between return periods from 5 minutes to 15 minutes?