Steve does have lots of stories to tell but those aren't the stories Feige is interested in having told.
I'm a casual fan of most of these character, and am only a devoted fan of Cap. And I may be all by myself in this but I've never really felt the movies did an adequate job of nailing Steve's idealism, or giving resounding examples of why people follow Steve. They just do, and we're required to accept that.
I don't understand the narrative of T'Challa apparently respecting Steve anymore than, considering their backgrounds.
Cap is my favorite character, too. And I see what you're saying. As much as I've enjoyed the MCU, they're are traits that Steve possesses in the comics that they could have done a better job of capturing in film. The fact that he's one of, if not THE greatest tacticians in the Marvel universe for one. We've really not seen that in full action yet.
They've also sort of just glossed over the 'man out of time' aspect of the character (I blame Whedon for deleting scenes from Avengers that would have really helped in that regard) and Steve's PTSD.
That said, they have done a great job with other essential aspects to Steve: his loyalty, his willingness to put what he feels is right over what's easy, his compassion and his sense of honor.
And I think it is those traits that explains T'Challa's respect. It would have been easier, for Steve, to leave Bucky, not knowing whether the programming was gone, to his fate. It would have been easier to sign the Accords, even if he didn't believe in them, just to keep the peace within the Avengers. Would have been easier to hide behind the Captain America mantle and be that trained monkey he so bucked against in the first film, instead of become essentially a fugitive. But he never did what was easy, he stayed true to himself.
He told Natasha that he had to be the one to bring Bucky in because Steve had been the only one on record to break through the Hydra programming. He knew that whoever was sent after Bucky wouldn't have as good of a chance of surviving that encounter as he did, and so he broke his very short-lived retirement and did that.
He could have sat back and left Bucky to his fate once the Winter Soldier was reactivated by Zemo, but he didn't do that, because he knew his friend was still in there somewhere and had figured out he was innocent of the UN bombing.
He could have signed the Accords when Tony offered that second time, even though Wanda was being falsely imprisoned and Steve had just been denied his right to council when he asked Everette Ross for a lawyer for Sam, Bucky and himself, indicating that the right to council wasn't a thing the Accords were respecting.
It was Steve's actions throughout the film that led to T'Challa eventually finding out about Bucky's innocence in T'Chaka's death and finding his father's true killer. By exhibiting loyalty and honor, Steve prevented T'Challa from having the death of an innocent on his hands. And considering what T'Chaka did to T'Challa's uncle and young cousin, I think Steve's unwillingness to leave a brother-in-arms behind no matter the obstacle, would make an impression on T'Challa.
That said, I agree with you on the idealism aspect. This is why I want so desperately to see the Nomad story reach it's conclusion in the MCU and get a proper ending. We haven't seen Steve say, not once "I'm not loyal to the government, I'm loyal to the dream" and why bother putting Cap in a franchise if you're not going to give at least one iteration of that
essential piece of idealism, one that defines his character?
Moreover, in the comics, as you are undoubtedly aware, it was Steve, as Commander Rogers - Top Cop, who eventually pardoned everyone who was on his side during Civil War and who overturned the SHRA and I really want to see that tied up properly as well. I feel, after living for a fugitive for a couple years now, he's earned that.