If I remember correctly, in WoE, Mind Breaker affects normal mDef as well.
Also, 70 mDef is easy to come by, yes. But you can't expect to be able to optimize against the one you're dueling. Walking around with mDef gears would leave you vulnerable to non-spellcasters, while a professor wouldn't need to optimize his gears to completely nullify other casters.
A "normal" professor should be able to throw out around 4k damage with a level 10 bolt at a mid-mDef char. So, we'll say 2,5k on someone with good mDef. Minus, 100'ish per hit for the int, we're down to 1,5k. Then we remove 60% of their int def, meaning you'll add 60'ish damage a hit again. Back to 2,1k. Double cast makes that 4,2k, plus insanely fast cast time, and stone curse (You're counting in heals from the pally, meaning you're not wearing ED). I still can't see what problems a professor would have against a paladin.
For champs, they can't do jack without their SP and buffs, and as a professor you could just keep dispelling and burning. Even if you burn your own SP, you've dispelled before that, so you have the time to get one SP click, and swap with them. I've never seen a good champ that actually have any more than 40-50 int, so in the end, you'll be dealing more damage on them with bolts than what you'd deal on pallies. They also have less HP.
SinX cannot kill anyone instantly. EDP-Link-SB is enough to get them down to low HP, but they'll live, and the after-cast delay from SB is enough for you to get raped by bolt spam, or any strong attack, really, since you're in a katar build (no shield, unless you're horribly quick at swapping, which most people aren't).
Paladins are great tanks, and they're pretty much the bane of Asura-spammers. But that's about it. Occult Impacts eats them in a few hits, they don't have any really strong attacks (MR kills 35% of their own HP in 5 attacks, if I remember correctly. IMO, that's pretty damn crappy), and their only real strength in PvP is based on luck (Chance of blocking damage, Gospel).
Champs are good, there's no denying that. But asura can be countered easily, and let's just all agree that 99% of the champ players out there use that skill, and that skill only.
I still vote for professor though.