Wouldn't a more apt comparison be someone armed with a 9mm pistol trying to take on a trained soldier with advanced anti-ballstic armor and plating, and an accurate rifle?
The only thing that would hamper modern soldiers is that from everything I have read medieval knights weren't possessed with any qualms about killing; life in general was much more violent than we experience now.
For more reading about this mindset, acoup.blog [0] has an excellent review of Bertrand de Born's work. What struck me is just how casual violence is treated, and that war is a treated as the expected normal condition. The peasantry definitely did not hold these views, but given that the nobility had a vast armament advantage and copious experience in killing I doubt many modern soldiers would be quite so callous. The only modern exception I can think of is child soldiers; but they have been subjected to abuse specifically to train them to be able to commit horrific acts. Maybe I am wrong, but I don't think most soldiers in modern militaries would easily be able to slaughter their countrymen with quite the same abandon. This is speculation, but I suspect that the nobles were able to do this because they viewed the peasantry as semi-subhuman; see the American antebellum south for the types of atrocities that that mindset enables.
[0] https://acoup.blog/2020/04/16/collections-a-trip-through-ber...
However this doesn't fit the "A peasant vs. a Knight" comaprison. A huge mass can also easily stop and defeat a knight.
No. A knight prone on the ground was very easy to kill very quickly - just stick a dagger through the visor. There is nothing comparable a civilian today can do to an APC.
Additionally, a single knight on a horse was not that hard to take down using relatively easily-available polearms, at least to a group of peasants. It doesn't scale down linearly - 40:9000 is a very different matter than 1:200, because a charge of 40 mounted knights is still inescapable death to the part of the enemy force they're charging at. A single knight would be much less terrifying even to a relatively group of peasants.
Armour in built up areas is very risky with out infantry support and the APC's would not be just driving around with out having dismounts supporting them.
Modern armor isn't invulnerable, but as I suggested it isn't easy to take out and likely would achieve similar to 40:9000 or worse in confrontations with civilians. Thankfully armor rolling over civilians like that isn't common enough for me to pull actual statistics, so we have to guess at efficacy compared to knights fighting peasants.
The armored vehicle analogy is apt.
Back to the analogy, a peasant (in the modern sense) is unlikely going to be as able to obtain an anti-tank or armor piercing rounds as easily as a peasant (medieval sense) could pick up a pike.
I'm certain that more than one knight died locked inside a burning barn back in the days.