be careful about reading too much into that hoops 101, especially considering how ancient it is. half the **** in those WIS made guides is wrong, at this point.
when you say, motion relies on passing, i guess i would disagree - you can get away with strong bh, solid but not great passing, more so in the motion offense than triangle or flex, IMO. obviously, passing is valuable in ALL offenses though.
i think fat has it right, the main difference is in how distribution works. lets see... you are in d2. yeah, you have to balance things more in motion, but not ridiculously more. also, in flex, a pure spd/per guard is going to be better for you than in motion. and a great ath/spd/bh good per guard is going to be better for you in motion, than flex. you can push a flex strong 3 point shooter to take more shots, and more 3s (+2 is no problem in the flex), than you could in motion. on the whole, if you have a very good, balanced offensive team, motion will serve you better, while if you have a couple stars, especially guards, and some really poor offensive players, flex will treat you better.