First of all, did the previous Avengers actually have *A* leader? It was sort of a group of peers. Unlike the comics where a formal leader (almost always Captain America) is picked. So to that extent, I'm not sure there WILL be a leader anymore than the previous group had one. But let's entertain the notion.
Hulk - I suspect Hulk is retiring.
War Machine (or some Iron Man replacement) - Seems unlikely as the character would not be a major one.
Captain America replacements - Falcon was given the shield, and Disney has announced a streaming TV show with Falcon and Winter Soldier in it. Which pretty tells you that Marvel does not view these characters as high end attractions.
Spider-Man - The Spider-Man franchise likely has the longest legs because it's still partly under Sony's control. Disney and Sony are cooperating. And Spidey is a MAJOR character. But as much as I love Tom Holland's portrayal, the MCU Spider-Man is a bumbling buffoon and a child. Not leader material.
Black Panther - This just seems natural. It would check the political correctness box. He's been in several movies already. The box office receipts justify it. We know a BP2 is already planned, and that tells you that Disney likes him. He's already a leader what with being a King. He's also not a power player...for whatever reasons the most powerful members seldom are the leaders in super groups, especially Avengers.
Captain Marvel - A CM2 is expected, but not formally announced AFAIK. She checks the political correctness box. She's got a military background, albeit not in a commanding role...or a command FOLLOWING role either. She's powerful as s---. BUT, I don't think the MCU likes her. Look at how they treated her in endgame. They wrote her as being arrogant, and borderline insulting the Avengers as if they weren't in her league. It's like Feige and the Russos were trying to alienate her from audiences. I think CM is going to be downplayed in the future. Just my hunch.
Dr. Strange - Certainly smart enough. But Strange is not really a team player. I suspect he'll be a major player in the big team ups, but I doubt he'll be dedicated to the Avengers like Cap and Tony were. He does have a 2nd movie coming.
Hawkeye - He was a leader in the comics, but it's pretty clear the MCU regards him as a supporting character.