WHY? Seriously what evidence do we have of that? NONE! Most of the trailers have been Ultron-centric, with only Tony, Hulk, and Widow really getting any kind of focus It in no way indicates that Whedon doesn't know what he's doing with Cap, at all.
And no, QS, SW, and Hawkeye have NOT "gotten more showcase" in the trailers than Cap. QS is in this new trailer for like half a second, as a face shot, and he has like two blink and you'll miss them moments in the first one. Scarlet Witch has only a few tiny shots as well. And Hawkeye got like a second of screentime in the first trailer, and less than that in this one. It's literally him running through the woods (first trailer) and leaning against a tree (this one). That's it.