Blighter gives up a lot of spell choice to get 9th level spells at 15th level. Those 9ths aren't that great either. Ur Priest looks easier to use to me, but the blighter is passable.
I agree, but the Blighter entries are looking much easier to me. Its not good if you want to "do everything" but it looks great if you can be a player that enjoys just having a lot of power in one particular area. I definitley am not debating how much better Ur-Priest is; we all know its better. I'm just trying to see how far I can go with and how optimized we can get with the Blighter (I've done similarly with Shadowcasters, Incarnates, and many others). If there were an Ultimate Magus for divine spellcasters, though, look out!
Plus, I'd have to say that the wording of the special requirement means to me that you'd have to get the 3rd casting as a druid somehow.
It states "Must be an ex-druid previously capable of casting 3rd level druid spells." Most DMs I know would interpret that as meaning spells from the Druid spell list, and we are capable of casting a 3rd level Druid spell in each of the builds I've put up so far, even with just 1 level of Druid. We're meeting your interpretation, too.
Anyways, thanks for the commentary; this stuff needs to be (re)stated on occasion.