One thing I noticed is that in Pacific Fighters campaigns, the aircraft simply race to the target. It's very difficult to keep up. Some of the missions also have you go further than your aircraft's historical range, and you will invariably end up in the drink.
In fact, on one mission pertaining to Wake island, my group of Wildcats went full throttle from take-off to the target area, where we met some Zeros coming head-on, also at top speed. My flight simply crashed into their flight, and I was mortally wounded from the ensuing explosions.
I haven't played a PF era campaign mission since.
Forgotten Battles era campaigns are nicer because after reaching their final altitude, the AI slow down to a reasonable amount, and you can easily fit into the formation with them. The only problem is that subsequent waypoints typically involve instantaneous speed changes which forces you to be on your toes. For instance "One minute to target!" results in every Ju-87 shedding 50km/h instantly, causing me to rocket past the group, and now I have to worry if I'm going to hit anyone, while trying to find my place in the formation again, while being shot at, and while only moments from the target, which I absolutely cannot miss because I've got only one egg to deliver, and I've been flying for an hour....
You could try to increase your rank at the start of a campaign to the highest level, or play user-made missions in which, hopefully, the cruise speed of the AI to certain waypoints has been edited from the default.