I think "peak human" needs to be properly defined.
As I understand it, "peak human" means that you're rubbing up against the absolute scientific limits of what can possibly be achieved, while still being classified as "human". An average human could train for their entire lives and maybe reach the level of "peak human" in one specific area. Cap is mostly supposed to be peak human in nearly every possible way. That combination of ridiculous strengths can result in feats that defy expectations, but which (scientifically speaking) could plausibly have been performed by a flesh-and-blood human being, even if no such human exists. And yet, Cap performs an assorted variety of those feats on a daily basis.
Batman is not peak human. Batman is far beyond what an ordinary human can hope to achieve, but that doesn't mean that (in any or all areas) his growth has been stopped only by the absolute scientific limit of his species.
I think Wolverine is a good example to talk about when talking about peak human. Wolverine's primary mutation is his healing factor, which largely gifts him with a nearly-peak human physique as a secondary side effect. Every time Wolverine wakes up and yawns, his healing factor-supported body responds as if he just went through a Rocky IV training montage, which is why Wolverine is constantly jacked. He has absolutely perfect eyesight. His fingers have the sensitivity of a professional safecracker, and his nose can be used to track people like a bloodhound, because his senses are as fresh and raw as a newborn baby's. These are peak human traits, and they didn't directly come from his mutation (they came indirectly from his mutation). Which is why they can't exceed the absolute limits of humanity. Although his healing factor gives him a boost to his endurance and stamina, which means that on the whole, Wolverine does go beyond peak human. He has poison and disease resistance which is beyond peak human. He doesn't age. His claws (and adamantium bones, when he has those) are more than human. Basically, the healing factor pushes Wolverine up to the level of peak human (as the Super Soldier Serum was supposed to do for Cap), and then Wolverine's mutant power pushes him over the edge into superhuman.
I think that Cap is mostly supposed to be peak human, but... maybe he's not? Maybe he crosses the line? The Super Soldier Serum brought him to the level of peak human (which means he could kick Batman's ass), but it might have pushed him over the edge into superhuman. There were some gamma rays used during the Super Soldier process, so it's possible that Cap might have a tiny bit of The Hulk inside of him, or perhaps the radiation triggered a mutation.
T'Challa by the way, was well below the bar of peak human (he was just a regular fit and well-trained guy), and then he used a superhuman substance (the magic vibranium flowers) to boost his strength beyond that level of ordinary. That DOES NOT mean that T'Challa's strength has exceeded the bar set by peak human. It means that T'Challa's unusual strength is not human in origin, and that it could plausibly exceed peak human (because it's running on a different track now), but it's not clear if it actually does or doesn't exceed the level of peak human.
