Well, I woudln't go so far as to say that Paladins and Shadowknights have the same spells. They have some similar spells, but for instance - Shadowknights get DoTs, Lifetaps, Pets, Disease Based DD spells.
Paladins, from what they tell me, do not get any pet, they get heals instead of lifetaps - heals can help others in the group, lifetaps only help the shadowknight. Most of a paladins spells are, unless I am wrong, divine based instead of disease/poison.
Paladins and ShadowKnights are similar, yes, but the same? No.
Yes, for the most part they wear the same armor, but who knows what there is going to be in the future, we may see alignment attuned gear, where only evil can wear such-and-such items, while good can only wear this other kind.
The game is still young, and to pass judgement on an entire game based off of a few months of play is, dont take this the wrong way, laughable.