You're also probably discounting what peasant style manual labor (and hobbies, which include beating the shit out of each other with fists, clubs, etc) does for your combat ability. Hand and wrist strength is a huge deal in pre-firearms days, and peasants were at least 3-4 standard deviations stronger in these ways than average people now (really: that much -I've fooled around with building hand strength and it's bonkers how strong people can get in this domain). People basically exerted their strength through simple hafted tools all day; makes them good at exerting their strength through simple hafted tools all day. Regarding group tactics; peasants had lots of games which could have helped them with this. For example, Hurling[0], and I'm sure there was lots of stuff like Calcio Storico[1].
The real advantage the knights had (beyond equipment, like horses and the morale of feeling superior to the peasant) was probably nutrition. They spent most of their downtime hunting, feasting and eating meat, and between wearing heavy armor and their strength oriented workouts, the knights were probably pretty jacked. 50 or 100lbs of muscle and fat and 6-8" of height helps a lot. I don't have references in front of me for this, but David Willoughby talks about some of this in his book, and I'm sure you can see it in skeletons of Nobles versus peasants (aka Nobles will have larger skeletons with 'deformities' at the muscle attachment points).