I will say there is less Steve Rogers (Chris Evans) and Natasha (Scarlett Johansson) than you might expect in this movie [Infinity War].
One thing that was entirely evident even before Avengers: Infinity War arrived in theaters was that there was going to be an insane amount of characters featured in the movie.
Captain America and Black Widow had very important parts to play in trying to stop Thanos from getting his hands on all of the Infinity Stones.
It looks like Captain America and Black Widow are two of the characters who are going to get more in Avengers 4.