I realized that nearly every other Vanguard directly counters Cap
I'm a vanguard main with mainly using Cap, Magneto and dabbling in all the others except Groot.
So I'm my many many hours i came to this realization of how every other tanks basically counters Cap.
Venom: Is more mobile with a faster cooldown on his dive and swing. Can basically extend his HP to 3x of Caps. Has a ranged attacks that cannot be reflected.
If you're trying to help your supports there's nearly nothing you can do to stop a Venom because he can literally ignore your minimal damage.
If you're attacking and a Venom is defending, you can't outtank any damage. Venom's slow reduces his mobility.
Magneto: Can literally make any Cap dive obsolete with using his shield in whoever Cap is diving. Can also use the shield on himself to out tank Cap but can also use his other shield to negate Caps damage because after 2 attacks, Caps attacks are considered ranged. More on this later.
Groot: Caps entire strategy is to get in, create chaos and get out. Good Groot players know this and will immediately wall off escape points. He can also outdamage Cap in a brawl and has ranged attacks.
Hulk: Can shield his entire team meaning your whole existence is pointless. If attacking your supports Cap can do nothing to stop him similar to Venom. He can also just stun Cap and walk right by because Cap has no CC. Also people say Caps pros are his mobility but good Hulk players can be any where in a huge radius in a second with his huge jumps. I used to chase Cap players down all the time with Hulk.
Thor: Cap pretty much can't so anything here. Thor can immediately displace Cap if he starts attacking the backlane. If they confront each other Thor outputs so much damage and gains a shield that Cap simply can't deal with.
Peni: Basically her whole kit is a Cap counter. She has a 3 second stun which she can use to save supports.
If she stands next to her spider spawner Cap literally can do nothing to her. The mines will kill him if he goes in, and she can attack from range.
Her whole nest can protect the back lane which means going in can be suicide.
Strange: Can outshield, out damage, outbrawl, out mobility, etc.
Strange combos of attacks, melee cancel and his burst does a lot of burst damage, easily more than Cap can do.
The issue is with Caps attack and how Magneto and Strange shields work that essentially gives them bonus resistance against Cap. Strange and Magneto shields cannot block melee attacks but can block projectiles.
Caps attacks turn from punchs to shield throws after 2 attacks. His next 4 attacks are now projectile attacks.
So let's say you have a Strange that is nearly dead. A couple more hits and he's done. You punch him through his shield twice and and only one more hit until he's dead.....except now you're not punching and his shield will actually block your damage.
The number of times a Strange has survived something like that because of Caps design kind of sucks. Typically by that point he will float out of your range and get healed to full health in .2 seconds.
Now you might be asking, why are you attacking their tanks?
I'm not suggesting that. I'm saying that in any situation where you're trying to attack, all other vanguards have some way to stop you easily.
However when enemy vanguards attack your team, you can do little to actually protect your teammates since they can shrug off your meaningless damage or walk by since you have no good CC.
The highs of playing Cap are high when you do have some good plays but the reality of it is that he is simply outclassed by every other vanguard.
Mobility doesn't mean much in a game centered around holding a specific locations or a slow moving cart. I imagine if there was a CTF mode he would excel there though.
Cap should be like the Soldier from TF2.
Good mobility (rocket jump/Caps jumps and dashes)
Good durability (Soldier 2nd highest HP/Cap high HP)
But what the Soldier has and Cap doesn't is CC and damage. The Soldier can knock people up constantly with his rockets and if accurate could easily do tons of damage. Cap can do neither of these so he just feels bad to play sometimes seeing other heroes just do his job better and make his meaningless.