@Cakedoctor537375 That's a pretty good theory. There's also another theory relating to the villains.
Avengers - Chitauri/Loki
Avengers: Age of Ultron - Ultron
Avengers: Infinity War - Thanos with Infinity Gauntlet
Avengers: Endgame - Thanos without Infinity Gauntlet
Avengers: Doomsday - Dr. Doom
Avengers: Secret Wars - Beyonder?