Loremaster PrC. If I no longer gain my Pathfinder Diviner special abilities, what would be the point of becoming Loremaster?
Ronin PrC. I can play a Fighter with more plusses to hit and damage, or a PrC that gives me some charge bonus and a tiny bit of sneak attack.
Warlock Base Class. yes, he can still go on forever, unlike the Pathfinder spellcasters. But compare him to an Evoker Wizard (let's not talk about the Sorcerer in Alpha 2. Normally I'd compare to him, but he is clearly not finished or balanced yet). The Evoker Wizard can cast several extra magic missiles now. Sure, it's a far cry from at-will, but he didn't lose much for this, and he still has his usual array of spells. The Warlock will work fine if you throw a lot of equal level encounters at him. But beware the more challenging encounters - the Evoker has some extra resources to spend here the Warlock just doesn't have. Fireballs, Disintegrates, Chain Lightnings. The fundamental problem of the Warlock remains (inability to "spike" in high threat encounters, and a low versatility), but the Wizards fundamental problem (to few spells to spare in normal encounters) is lessened.
Maybe both classes are underpowered. But they are classes I always felt tempted to play.
I think most people would say that Loremaster was "overpowered", strictly speaking, but not in a game balance altering way. The Pathfinder Diviner is definitely better then this.
You might say the differences are small, but I just disagree. A potential +3 to-hit & damage difference between a Fighter and a Fighter/Ronin is just not small anymore. If you think otherwise, then this is something we will never be able to agree on, and it explains why I prefer the idea of 4E over Pathfinder.