system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel/Avengers] How in the hell does Captain America stay relevant?

He's a peak human with a shield. That's it. He's far outclassed by everyone on the team and I seriously wonder why he just doesn't give the shield to someone who's more capable like, say, Iron Man. Even Batman understood that just "being there as a leader" ain't gonna do shit when the local Death God 9000 comes around, so he built some big ass suits that buff him up to stay relevant. Cap has none of that. Just a shield.
gpt
Cap is a master of what sports scouts call 'the intangibles'. 

He has leadership ability that inspires everyone who works with him to new heights of accomplishment. People just plain fight harder with him present. His loyalty to them and the team in turn provokes rabid loyalty to him, as well. You will not harm Steve Rogers without dealing with a lot of his very unhappy friends shortly thereafter.

He has tactical skills that allow him to coordinate multiple superpowered people with near perfect efficiency, which itself is a force multiplier.

He is an unparalleled combatant, capable of fighting much more physically enhanced creatures using superior technique, insane levels of agility, and knowledge of fighting arts.

Physically, in the MCU there's really no way to get around it, the stuff he does is straight superhuman. He may be 'peak human', but he operates at a level no human ever has operated at.

And then you say 'just a shield'. That shield is a disc of the toughest material on the planet. A material that defies physics and renders him invulnerable when properly used. Not to mention it is a fierce weapon in Cap's hands, and Cap can do things with it no one else can. That shield can deflect anything his more powerful teammates and opponents can dish out, and hurt them pretty badly if they're not very careful.

So others on the team have some attributes far beyond Cap's. His particular combination of attributes make him invaluable on any team he's on. It helps that he's no slouch in a fight and will always be found leading from the front and taking on the brunt of the enemy attack.

Death God 9000 might show up, but when it does it'll find Cap there, with that shield, a plan and some friends, and when it tastes that vibranium across it's grill, it may not be quite as easy to brush him aside as it thought.