Rainbow Dash MAY be faster than a fighter jet, perhaps even more dangerous, but that's because she's unique prodigy; the fastest flier in all of Equestria, the only pony capable of a sonic rainboom, most powerful pegasi by default, etc. She's the exception, not the rule.
If it ever comes to a pegasus/jet-fighter aerial dogfight, I'll bet on a jet fighter any day.
Thunderlane: "That's why we won't fight fair, if that ever happens. Hit those contraptions while they're on the ground with a few well-placed lightning bolts to the fuel tanks...or just to the ammo depots on the airbase. Maybe just stay low and avoid their fancy radar things, then have a team of pegasi whip up a tornado when the flyboys get into OUR airspace, while we burn away and let nature do its own work. It's a longshot, but we have ways of hitting back."