1. They Fight The Hulk A Lot
During this period of the Hulks characterization, he was less a mindless monster and more a really big jerk. Hulk wasnt fond of shouting smash! and referring to himself in the third person; he was more likely to monologue about his hatred of the entire human race. Though he was officially a member of the team, the first handful of issues or so had him fighting against the Avengers as often as he fought along side them. In one issue, Hulk even teams up with Namor after bonding over their mutual hatred of all things human.
When Captain America joined the team, the direction of the book changed, becoming more about a team of specialized individuals rather than a loose association of misfit heroes. Any team where one member kind of hates everyone else and constantly flies off the handle isnt very sustainable. The Hulk was eventually phased out to tell more cerebral stories with characters like Caps enemy from the war, Baron Zemo, and the powerful Kang the Conqueror. With that, the book started down the path that would lead to its iconic status today.