I've personally had opposite experiences with thunder/ice spells on genbu as you drak. Wiki lists both as weakness, perhaps just coincidence both ways?
According to testimonies on the wiki page: Diabolous Pole offers a 25% damage boost in dyna, but it doesn't offer any M.Accu %
So while you might see bigger numbers once in a while, the average will still favor even the NQ staff.
As far as my own personal experiences with drain/aspir, I've never seen them to follow any sort of macc rules whatsoever. I've landed large drains and aspirs on some of the most magic resistant mobs in the game, while I've seen multiple 0 drains and aspirs *without full HP/MP* on the least magic resistant mobs *yes I'm referring to mobs WITH MP also and not undead mobs*. I'm interested in the diabolos pole myself now, if even just to test it.