I'm so sick of this. I'm a Holy Priest, and I can say from my first hand experience that Paladins are great healers. An well geared Paladin can put out consistent HPS on a single target for a much longer period than a Priest can with FoL spam. Can put out equal HPS, but not consistently, because we are much more bounded by the FSR and our B&B heal is GH.
IOW, Paladins are on par with Priests in terms of healing, but we're designed for different different circumstances. If someone tries to play a Paladin like a Priest (ie, using Holy Light as their primary heal), the Paladin will suck at healing; similarly, if someone tries to play a Priest like a Paladin (ie, using Flash Heal spam), the Priest would be OOM so fast it's not funny.
As for your assumptions about Death Knights, they're probably just as foolish. Protection Warriors and Feral Druids gain aggro through physical damage, and their threat building is limited by how much rage they can generate. Protection Paladins gain aggro primarily through Holy Spell Damage with a little melee thrown in, and their threat building is limited by how much mana they have available. I imagine Death Knights, as tanks, will be much more like Paladins, except using Shadow Damage, but their threat building will be limited by Runes which, as I understand the most recent rumors that they put different ones on CD depending on which abilities are used, will be substantially different than any other tanking class so far.
But to answer the question in the title, will they be over-powered? Maybe, maybe not. Class balancing is difficult, and Blizzard is still tweaking it with every patch. Besides, different classes and builds excel at different things. So it's entirely possible they'll be great for PvE and terrible for PvP, or vice versa. Or maybe they'll be mediocre tanks, but great DPSers, or vice versa. But Blizzard says they will not be more powerful so I imagine, if they are over powered at first, they'll be substantially nerfed. So it really doesn't matter.
IOW, Paladins are on par with Priests in terms of healing, but we're designed for different different circumstances. If someone tries to play a Paladin like a Priest (ie, using Holy Light as their primary heal), the Paladin will suck at healing; similarly, if someone tries to play a Priest like a Paladin (ie, using Flash Heal spam), the Priest would be OOM so fast it's not funny.
As for your assumptions about Death Knights, they're probably just as foolish. Protection Warriors and Feral Druids gain aggro through physical damage, and their threat building is limited by how much rage they can generate. Protection Paladins gain aggro primarily through Holy Spell Damage with a little melee thrown in, and their threat building is limited by how much mana they have available. I imagine Death Knights, as tanks, will be much more like Paladins, except using Shadow Damage, but their threat building will be limited by Runes which, as I understand the most recent rumors that they put different ones on CD depending on which abilities are used, will be substantially different than any other tanking class so far.
But to answer the question in the title, will they be over-powered? Maybe, maybe not. Class balancing is difficult, and Blizzard is still tweaking it with every patch. Besides, different classes and builds excel at different things. So it's entirely possible they'll be great for PvE and terrible for PvP, or vice versa. Or maybe they'll be mediocre tanks, but great DPSers, or vice versa. But Blizzard says they will not be more powerful so I imagine, if they are over powered at first, they'll be substantially nerfed. So it really doesn't matter.