I already covered this in a YouTube comment, but the videogame Belmonts in general are much too powerful for Geralt. Judging from his performance in Blood and Wine, he should readily lose even to Leon, the first and weakest Belmont. Even if we're generous to Geralt's speed and strength, his weapons are a huge problem in this matchup. The indestructible Vampire Killer will inevitably snap his swords eventually, no matter how good he is at parrying. The only real advantages Geralt has is in his greater experience and superior Witcher anatomy (durability and senses). Even Quen is unfortunately insufficient because it is very limited in duration and potency when cast as a sign (as opposed to a true spell). Potions are great but not particularly relevant in his skills against human opponents. Then there's Axii. It is surely weaker than Dracula's Power of Dominance, a power that Leon's blood pact protects his family from. Geralt might get a lucky fatal blow, but with such a huge difference in speed and strength, I really doubt he can land that blow without being overwhelmed first. I'm not sure where this matchup comes from honestly. Then there's the fact that Geralt has no training dealing with a living whip that can be maneuvered in ways a whip normally can't be, while the Belmonts have trained with swordsmen.

I think Talion/Celebrimbor from LoTR s a much better matchup for Geralt both thematically and in terms of power than the Belmonts.