Vinland Saga doesn't have any calculations made for it, so Thorkell is only as powerful as
this feat.
Thorkell's experience is comparable to Wardens, if not higher. Thorkell has fought and won enough battles to get to the point where he was "tired of being on the side that always emerged victorious." Thorkell went evenly matched against Garm, who is able to kill armed men as a child and was implied by Garm himself to be holding back in the fight. Floki, who's known Thorkell years, thinks that there is no man alive that could kill Thorkell. Floki's statement has some merit, as he is a commander of the Jomsvikings, an army that is made to go around and fight wars. In the minimum of two years (Since Floki has known him for years, so more than one) Floki has not seen one warrior of comparable strength or skill to beat Thorkell. This experience has a timeframe of more than ten years, coming from
Thors deserting the Jomsvikings "more than a decade before." (Look at his abilities section or press Control + G and search "decade") The Jomsvikings are regularly active in battle, leaving Thorkell sitting at the second top (first place being Thors) in terms of strength and experience. There's more examples to be pulled that Thorkell is no sloth in experience, but I'm sure you get the point.
In the actual "crossing weapons" fight, I'm not sure if Warden could just cut through Thorkell's axe and armor, but assuming he does, if the first one isn't a kill shot then Thorkell could grab and pop Warden's head like a grape.
My vote goes to Warden even despite this. Thorkell has the capacity to do some genuinely stupid things, even with Standard Battle Assumptions. Thorkell lives for the thrill of the fight, so he will absolutely prolong or hold back to make the fight longer, causing Warden to reach his win conditions more reliably.
Also what does Warden do against Thorkell's Fear Inducement?