How many AA missiles does an F-35 hold, 10? 20 Cessnas would certainly be able to take down a lone F-35 in favourable conditions. Quantity has a quality of it's own.
This is ridiculous. A Cessna 172 might be able to suicide into a parked F-35, but the idea that 20 would be able to engage it in a dogfight and win just shows a complete lack of aerospace knowledge.
Dogfighting is a thing of the past. 20 Cessnas approaching from different directions, with decently ranged AA missiles ( which is the point of the discussion, OP compared drone performances to a Cessna, and everyone is going in on the allegory, but the real question is if slow drones would be able to tackle an F-35, and the answer is it will depend on their armament, but probably) could overwhelm an F-35.