They have plenty of humor throughout the MCU. RDJ being Tony Stark simply took it to the top. A guy who legitimately feels like a billionaire, genius, playboy, philanthropist. Lang can't replace any of that. He may be a genius-level engineer, but Stark was basically the most intelligent man on Fake Earth.
As Far From Home conveys - no one is going to be the next Iron Man. It'll be a group effort from guys like Spider-Man, Black Panther, Ant-Man, etc that 'replace' that feeling. It's just too large a task. Replacing both Iron Man and Thanos.
Captain Marvel doesn't seem smart. She doesn't have the charisma of a 'playgirl'. She isn't gonna be a tech (rich) resource for the Avengers. She's definitely no philanthropist. She ain't replacing Iron Man.
I think audiences like more 'self-made' characters. Iron Man created the Arc Reactor and his suit. Steve Rogers created the man that embodies Captain America. Banner created the Hulk. Captain Marvel isn't interesting. No more interesting than Scarlet Witch (who has a more-storied history within the MCU, is getting a D+ show, and will be co-starring in a Phase 4 film).