Why wouldn't he stand a chance against a Lycan Jason? Alexander Corvinus was supposedly the only one strong enough to stop Hybrid Marcus. And the only ones who beat William and Marcus were Hybrid Micheal and Hybrid Selene.
That means that even as a normal lycan, his immortal status puts him several tiers above turned lycans and werewolves. So a turned jason would only be slightly stronger than a normal werewolf.
I believe the Lycan curse increase to a particular degree what the human base stats are at to begin with. Normal men becoming Lycans are the norm. A zombie with a demon inside of it, with the strength to punch a person 20+ mtrs at burst speed into trees Jason should become an immensely powerful Lycan wouldn't he?
There's also the disputed feat that Jason gets stronger everytime he dies.
Silver should have no effect on LycanJason.
Jason with enhanced strength, speed/agility, rapid regen, more bulk on top of his already zombie damage soak could be more than a match for William.
In regards to Alexander Corvinus we didn't see any feats from him. Such plot twists like the blood upgrade and the idea that only Selene and Michael are the only ones strong enough to to fight the duo are mute due to Jason being are foreign character to the universe.
check out the first scene in this video. Jason swings with one arm and look what happens to Kelly Rowland. Add a Lycan's longer reach, strength, and speed.
That makes sense, as Raze was strong enough to hurt a Werewolf when he was still a human. And I'm guessing it's disputed because it's not clearly specified or shown, so that can't be used since it's assumption. And feats or not, Selene knew Alexander was the only one who could stop Marcus, and Alexander confirmed it. Saying that while he could, he refused because despite the fact that his sons were monsters, they were still his sons. So that means that as the original immortal, Alexander was more powerful than his enhanced sons. Which would also mean as he passed his immortal blood on to them, they would get some natural measure of strength which was increased when they were changed. A fully fed William would be more than a match for Jason, and take a majority over werewolf Jason. Hell, if Jason turned chances are he could be driven mad by the disease as well and start following William.