First things first, they're in character, their speed is equalized, and Inosuke's first key and Thorkell's second key are being used. Okay.
Question: The first key of Inosuke, that's him before he Spider Arc, right? Because I remember him getting absolutely stomped by the Spider Father Demon, who
like Thorkell, can use tree trunks as weapons. Inosuke was
amazed by Tanjiro being able to cut down one tree (something that Thorkell is casually able to do) and the Spider Father then proceeded to
smack Tanjiro with the tree trunk away. Thorkell's first key is already able to do that,
using tree trunks as weapon.
AP: Thorkell is able to casually slaughter 400 vikings in a short period of time while also slicing trees apart, can easily destroy wooden and stone walls with his fist, can easily kill a bear barehanded, bulldoze 2 houses, and it was said that 4000 men aren't enough to stop him. Thorkell has so much physical strength that he can uppercut a horse with a person on it, with 3 fingers, and he can kick a person 40 meters into the air.
Lifting Strength: Thorkell's lifting strength is easily superior. Even the lifting strength of Inosuke's third key is questionable cause that's something Thorkell would also be casually able to do.
Striking Strength: Same as AP.
Durability: No clue.
Stamina: Thorkell. The stamina of Inosuke's first key is very high while for Thorkell, it's extremely high, for obvious reasons that are stated in his profile.
Intelligence: Thorkell. He's way smarter than he appears, has way more experience, and was able to deal with Thorfinn (An assassin), who's much smarter than Inosuke.
Weaknesses: "Inosuke is very bull-headed and rushes into fights without thinking" That's exactly what could get him killed. It's what almost got Thorfinn killed, he rushed towards Thorkell who then almost one-shotted him. As for Thorkell, he has a tough time against little, agile guys, but we already saw with Thorfinn and Garm, that even that doesn't stop Thorkell. In Thorkell's first fight with Thorfinn, he whooped him, In his second fight, he whooped him again. He also kept up with Garm, who blitzed Thorfinn. And mind you, Thorfinn (5'0) is shorter than Inosuke 5'5).
As for Pain Tolerance, there's no way Inosuke's Pain Tolerance is anywhere near Thorkell's, he was in pain when the Spider Father squeezed his head, no? Thorkell on the other hand literally didn't have any sort of reaction when Thorfinn cut 2 of his fingers off.
Tbh, I find the argument of "Thorkell is skilled with an axe but Inosuke can dodge, Barbaric dude vs Dude thats flexible as hell, Inosuke can dodge pretty easily" really stupid because Thorkell already proved that wrong numerous of times. He isn't just a barbaric dude, he's very fast. In his first fight against Thorfinn (a short and agile guy like Inosuke), he fought Thorfinn
barehanded and Thorfinn had to actively dodge his punches. Also, when Thorfinn got him off balance and was planning to stab Thorkell in his face/head, Thorkell was fast enough to
put his hand in front of him to prevent that. Even years after that, a Thorkell who's almost 60, misses 2 fingers and an eye,
kept up with Garm who
blitzed Thorfinn. Thorkell is fast asf.