I actually do agree that they've done a pretty lame job at developing Steve and Tony as anything beyond aquaintances.
I prefer good writing and seeing a friendship grow rather than being told 'so were we.' Ya know, the same good writing that has organic friendships between Cap and Bucky, Cap and Thor, Cap and Black Widow, Iron Man and Hulk, Iron Man and War Machine, and Cap/Falcon.
Now if you'd said 'Cap and Stark are brothers', you'd have foundation to stand on. But eh, you watched BvS and thought Batman was literally saying he was friends with Superman instead of comforting a scared woman with something to put her at ease. Which was hamfisted and obvious but still utterly missed by you.
By that logic, Steve and Bucky's friendship is also under microscope. How much is good enough to tip over that line between friend and acquaintances for you?
Do share with us your ideal friendship montage ideas.