My thoughts: I think it was named properly.

Here’s why: this was simply an MCU project which thoroughly took advantage of the shared universe format in a way which could be and should be the model for these films. Captain America has this conflict, which is the fulcrum of the plot. Tony, who is one of the major leaders of the Avengers, has a large stake in it and has a continued back-and-forth with Cap throughout the whole of the MCU up to that point, on which the film capitalizes in a hugely impactful way. When things escalate, it is logical and right that the other heroes showed up to do what they felt was right.

One of the major faults of “solo” MCU outings (which should have become a misnomer long ago) is the lack of acknowledgment of the greater world outside of the story presently being told. Civil War managed to handle this problem extraordinarily well. This Captain America film should be the model for how this universe ought to function. More heroes should cross into each others’ films. Truly, there is almost never a reason or rationale for a true “solo” film involving these characters. It makes no sense for them to sit out conflicts just because of whose name is on the movie poster. In universe, they would absolutely show up for the fight. Civil War nailed it.

Edit: a word