My recall of my final 10spd days (5x2) and observation of downtube shifter riders
since, is that the rider adjusts the cadence through a lot wider range in response
to terrain in preference to reaching down and shifting. With an 8-9-10spd
brifter it is so easy to change gears that cadence remains in the same small
range (for me 70-85 on single) rather than 45-90 with downtube shifter and
5 spd freewheel.