Sigh..... let's see where do i start...
Light arts has an inate fast cast attached to it...tho it isn't as strong as fast cast from rdm it is still considirable enough to use over /rdm because it's a very minor diffrence.
/sch already has dispel..you just need to use dark arts and black addendem, free dispel is the only good thing about /rdm but in all honesty, that should not be your priority as whm outside procing yellow in abyssea.
refresh on others? if a party needs refresh that badly they can get a rdm or hell, even get a blm/rdm to do it. that is not a valid excuse for /rdm if a blm in the party they can usually refresh them selves, pld? lol won't even get into that.
need i go on? seriously, it sucks. you depend entirly on refresh because you are running out of mp TO fast. i don't want to get into this with another whm again..try the 2 one day extensivly, and see which one is truely better.
Orison pants +2 in no way makes up the 10% Mp cost reduction light arts gives to ALL spells....
if you still have trouble figuring it out the primary reason /sch beats any other sub is because of that 10% recution on TOP of the conserve Mp trait /sch has. as well as sublimation /rdm can not come close to that to a good whm, even with the false hope convert.