it does seem that duke is somewhat underrated, but i think hancock has him beat.
they both have had long and varied careers. i think duke's best is up with herbie's - brazilian love affair is as good as anything in hancock's catalog.
but hancock has a lot more. i mean, hancock has written jazz standards. where's george duke's 'cantaloupe island' or 'watermelon man'? and then the headhunters were hard to beat.
and then herbie with miles is a helluva lot better than george duke with miles.
but still, george duke has some killer r&b stuff and did great work with zappa.