It made sense to get rid of Task master. She was a badly written character compared to how walker was written, we were ment to hate him. Gender swaped him, the mcu writters acting like black widow(s) couldnt have fought the comic accurate Task Master. Also there would have been too manny shields flying around.

Yelena was giving steve Roger's of vibes. Going into the void head on and not running away.

Bucky was Natasha of the group. Her role in winter solider/ civil war. They both had little screen time but we're their at the center of it all

Ava was the iron man persona. She would go of on her own but still helped them out. Her suit/ mask was giving vibes from the game Destiny ,the warlock class.

Red guardian was the Thor of the group, with how he would express himself and talk .

Sentry was a mix of Thor and hulk. He had his funny moments but than you find out he has a duel destructive persona like hulk.

Us Agent was useless, like Hawkeye was written in the earlier movies. He is the weekest super solider of the 3 even if RG seems weaker in power. RG and Bucky have experience/ training

I feel the mc aged Sam up. Isnt he sometimes depicted as someone far younger than captain America and Ironman, maybe just a little older if not close in age with spiderman.