To answer your question, yes, a staff (2-Hand) can be more powerful than a wand (1-hand), but it really depends on what weapon your comparing, what skills you have, what your trait points are, and where you are in the game. So... comparing wands and staves is not a clear linear process.
Wands, which are one-hand weapons for mages, allow the use of an off-hand item, either an orb or shield. As such, wands are considered the more defensive build for mages. Wand use can be improved through the skill Wand Mastery.
Staves, which are two-handed weapons for mages, tend to do more damage but dont allow the use of an off-hand item. As such, staves are considered the more offensive build for mages. Staff use can be improved through the skill Staff Mastery.