I think BOTH Bucky and Sam make for poor replacement Caps, personally. Idk, maybe it’s just my general bias against legacy characters outside of a few rare exceptions, but Steve Rogers was Cap because his story was epic and unique. The MCU even hammered home the notion that people had tried for 60 years to recreate the magic formula that created him and couldn’t do it because Steve himself was the magic ingredient.
And then all of a sudden it’s like, “actually, either of his best friends could do it. They’ve got skills!” Nah.
But then as mentioned, I’m just not a fan of superhero identities being mantles to be passed down, unless you’re a Lantern and it’s literally a job or something. But especially not for someone like Steve for whom the point of the story was “WHO YOU ARE is what makes you irreplicable.”
Bucky is Winter Soldier. Sam is Falcon. They can be their own leads with those identities imo.