Let's see . . . the whole thing about Bucky centered more on his impact upon Tony Stark than Steve Rogers. In fact, not only did the movie started with the murders of Howard and Maria Stark, but the whole movie centered around using Bucky's role as Winter Soldier and the Starks' murders in order to break up the Avengers. The movie spent ten to fifteen minutes on Tony recruiting Peter Parker for the battle in Berlin than it did on Steve and Sam recruiting Clint Barton and Scott Laing. In fact, why would Scott suddenly volunteer to help Steve and Sam without really knowing them? Why did Clint end his retirement to help those two? The movie never bothered to answer.
Most of this is actually you complaining about the shared universe of the Marvel films. Scott and Hawkeye don't really need to be explained that much, because we've seen it in previous films. Scott less so, but his Avengers-nerd moment with Falcon in his own solo pretty much sets all the groundwork you need. They're banking on the audience being familiar with these characters already, a conceit of the shared universe.
Tony recruiting Peter isn't about Tony, either, by the way. It's the one really blatant moment in the film where they jettison the plot for the "cool factor" of introducing the MCU's Spidey. If that isn't enough to get you through the tangent, and I understand it isn't for many viewers, then so be it.
And as for Steve and Bucky, of course the movie didn't center on Bucky's impact on Steve. That was what Winter Soldier was about! This took the next step: if Bucky is back in the world, but he was the Winter Soldier for a really long time, what does that look like. Bucky's impact on EVERYBODY ELSE is the point, and Stark is used as the focus because, again, he's a character the audience has already connected with. Bucky did bad things. This will have consequences. Steve will face choices.
This movie DID NOT strike me as a real follow up to "The Winter Soldier", since it didn't really bother with Steve trying to reconcile with Bucky, aside from a long conversation about the Winter Soldier program. The relationship between Bucky and Sam - and their relationship with Steve - was treated as a running joke. And Steve's romance with Sharon Carter was nothing but a rush job.
On the Sharon Carter bit, considering all we've seen of their romance is the meet cute and their first "date", I'm not sure I'd agree about things being rushed. That said, I'll concede the point. It was a sub plot that has rolled through both Winter Soldier and Civil War (see, another way the one is a sequel to the other!), but it's not the focus.
Steve didn't have to reconcile with Bucky. The whole point of the Winter Soldier's climax is that Steve still loves Bucky, and doesn't want to fight him once the world is saved. Bucky needed to reconcile with himself, but we actually do see that in Civil War, as he goes from isolating himself to standing shoulder to shoulder with Steve once again.
And yes, the relationship between Bucky and Sam was played for laughs. It's two guys who both share the same best friend, and who couldn't really be more different. They don't like each other, but they'll play along for Steve's sake. The humor conveyed the point as well as any deep conversation could have, and saved on running time. But I can't in any way agree that their relationship to Steve was played as a joke.
End of the day, you'll like what you like, and won't like what you won't. The movie wasn't the sequel to Winter Soldier you wanted, that's fair enough. But your argument that it wasn't a real follow up is bunk. The movie pays off plot threads from both previous Cap movies, and Steve is the emotional heart of the film, not to mention the primary actor. His choices drive the film's plot, his relationships define it's stakes, and his failures and successes circumscribe it's outcomes.
