Deliberate mistake: On the Hawkeye's radar screen, the Bandits virtually stand still after switching course to defend target (after destruction of the enemies' runway). While the Daggers complete their way to the Uranium plant, destroy it, evade the SAMs and return (save for Maverick, who got shot down), the bandits are still in the same place. This is a deliberate error: If the Bandits had progressed with normal speed, the Daggers couldn't have possibly avoided a confrontation on their way back. (01:34:42 - 01:40:30)
Continuity mistake: When Maverick calls Comanche, the sun is behind the Daggers. When they descend below radar a few seconds later, the sun is ahead of them. (01:31:16)
Answer: The real-world answer is that F-35s only come in single-seat configuration, so there was no way to put the actors in one seat for filming while pilots flew the plane. It would also make for less of an "underdog" feel of going up against overwhelming odds. The in-universe answer is that F-18s are better suited for the kind of mission it is.