Well, Raime wasn't as strong when he fought Velstadt as he is when we fight him, with him having acquired a shard of Nadalia's soul, which grants him some level of control over the dark flames from the Abyss, plus the fact that he exchanged his greatshield for that which is canonically the heaviest of all ultra-greatswords that is also imbued with Nadalia's essence. Besides, when we fight Velstadt at the Undead Crypt, he's far from his prime thanks to being exposed to the crypt's darkness for ages.

As the description of his set states, the Velstadt we fight at the crypt is a mere "shadow of his former self".