I admit I had to google DS2 bosses because I couldn't remember half of them but this isn't true at all, even discarding the dlc.To be fair, he is the hardest boss I fought in DS2, never finished it after 72 hours. What a chore >.>
Vanilla DS2 has Darklurker, Ancient Dragon and Veldstat. Also Smelter Demon if you're pure melee.
DLC has Fume Knight, Sihn and Sire Alonne.
Pursuer is hard the first time you meet him but I think he's actually a great character and an enjoyable fight each time you face one of them. The fact they show up multiple times throughout the game also makes sense lore-wise.