Ant-Man 3: Everything It Needs To Fix About The Franchise
4. Bring In An Unexpected Avenger
If we're looking for a significant jump in quality between a second and third film, we should really be using Thor: Ragnarok as a template. One of the major reasons fans were interested in going back to another Thor film was the inclusion of The Hulk, with their fight scene on Sakaar being one of Phase Three's highpoints.
Similarly, as all the characters in the Ant-Man films are well established, featuring an Avenger as a side character would provide some much-needed spice. There's also already precedent here, with Falcon showing up in the original Ant-Man for one sequence, so it wouldn't be too much of a leap.
Picking the right character for this is key though, as they need to be well known enough to make an impact with fans, but small-scale enough to fit in with the series' tone. Taking all the mystical and cosmic MCU characters out, ground-level agents like Maria Hill and Nick Fury would've been great, if they hadn't already been in Spider-Man: Far From Home.
While someone like Shuri or War Machine might work, it's Hawkeye who feels more of a natural fit, if not only to expand on their rapport from Captain America: Civil War.