No, they’re not.
There’s more to just the physical pain associated with light use and undead. Yes, that’s the primary downside, which is worse than priests, because when a priest uses the light it is like a torch. You can turn it off and on, so it’s like a fire they can put out whenever they choose. Paladins do not have that same benefit. For them the torch is always on, so imagine a pain like fire coursing through your veins every moment of every day. That is what a Forsaken Paladin would go through.
But the more part is equally bothersome. See, when an undead dies and is reanimated they do not have certain senses returned to them. Their sense of taste is completely gone, as is their ability to feel as their nerves are dead and their ability to smell is non-existent. All of those senses return when they start using light magic. The ability to feel returns first, starting with the pain, but then it gradually gets worse. If they’ve got carrion beetles or rats in their body, gnawing at their dead flesh, they’ll start to feel that, and I don’t know about you, but I hate the feeling of insects crawling on me, I don’t know if I’d be able to deal with insects crawling IN me.
Then their sense of smell and taste returns, so suddenly they begin to smell all the rot and decay they exude, as well as the rot and decay of the places they live in, such as the Undercity. Places like the Undercity reek to high heavens of rot and decay (not to mention the smell of all the green alchemical discharge that makes up the canal ‘water’) so now they get to smell all of that. And finally their sense of taste returns, so if their mouths are full of rot, filth and decay, as is expected given that they’re undead (and I’m 99% sure dental/mouth hygiene isn’t on their priority list) then they start to taste that.
I don’t know what that would feel like, but I imagine if I started tasting rot and decay I’d want to gag and throw up.
So imagine you’re going through all of that. The pain, the ability to smell and taste rot and decay and the feeling of carrion beetles, rats and worms in your body eating at you. Then imagine you can turn all that off if you just refuse to use the light, if you decide “Nope, don’t want to be a Paladin or a Holy Priest, screw that!”
And now you might get an idea why the majority of Forsaken priests are Shadow Priests and why there are no Forsaken Paladins.