Oh I got my BoED classes mixed up.
I can answer the question then:
Permanent alignment shifting powers with a DC set my a Diplomacy check. It's like a Diplomancer with an even stronger weapon.
Nailed it in one. Well, two, sorta.
Yeah, I was the one that tossed out that rating in the first place, and it was mostly in the "omgwtfbbq"ness of having DC set by Diplomacy, possibly the #2 most easily pumpable skill (short only of jumplomancy). And "Conversion" is a campaign-ender. By JaronK's system, they occupy an odd space; they're weak in a lot of ways and can be a total dead weight in need of serious DM handholding, but they can also go totally off the rails with terrifying ease. Never, ever let an Emissary have a large audience. Given a soapbox and a month game-time, he can turn an entire city Lawful Stupid.
Even without that, "Calling" is pretty much an auto-stun against all non-undead evil creatures in a 30' radius. Technically it has a save, but any half-decent effort is getting you a DC of 30+1d20, even at low levels.
Mostly it's about the "Conversion" though. Srs hax.