Ace Combat 2's Infinity+1 Sword, the XFA-27, could launch four missiles in one go. While mild compared to pretty much every other one of the AC 'Breakers, it did make ground attack much quicker.
Ace Combat Zero: The Belkan War has a mild version of this in the Su-37 Terminator, which has a huge standard missile load, can equip the second-best missiles and best bomb in the game, and can turn on a freaking dime. There's little reason to fly anything else once you can afford it. The Eurofighter Typhoon is available even earlier in Mission 3 but only on the Mercenary Ace path (which is supposed to be harder than the Soldier or Knight paths), and it doesn't carry the Fuel Air Explosive (FAE) Bomb... which allows one to finish the Hresvelgr in three hits and Avalon (one of the infamous tunnel missions) in a single fly-through. Part of the issue is that the Terminator's available so early — complete Mission 6 on any path, any difficulty — whereas comparable or better planes can only be purchased after beating the game at least once, or have their requirements lowered if you have saves from the other two PS2 Ace Combat games on your memory card. Zero has a much less mild version of this in the ADFX-02 Morgan, which has a weapon that can finish some entire missions with a single shot. (Then again, it is the final boss' plane, and he's already demonstrated its nastiness on you...)
In Ace Combat games, the only actual restriction on the "superfighters" — the X-02 Wyvern (4, 5, Zero), the ADF-01 Falken (5, Zero), the ADFX-01 Morgan (Zero), and the CFA-44 Nosferatu (6) — is price to buy and unlock method; there are comparatively powerful late-game planes that are balanced in both ways, but the Su-37 is an exception.
Ace Combat 04: Shattered Skies had Quick-maneuver Air-to-Air Missiles (QAAMs), which were true "fire and forget" guaranteed air-to-air kills. While these are toned down in subsequent games, up until Ace Combat: Assault Horizon where they get a re-buff, in 6, they're usually considered a "n00b" weapon that online can only be best countered by... yep, bringing your own.
Ladies and gentlemen, meet the Su-47 Miki-EX, which, while being DLC, is a god tier aircraft because of its crazy mobility at over 600 miles per hour and boatload of QAAMs. In fact, any of the The Idolmaster aircraft could be this because of how much ammo they can carry, abilities and stats be damned.
The final mission of Ace Combat 5: The Unsung War is against eight of the toughest enemies in the game. It is intended to last at least thirty seconds for even the best players. However, take any plane that uses the XLAA, and you can one-shot-kill four of them from beyond their range, then perform a loop and one-shot the survivors. The game literally breaks if you do it right, as since you are not meant to beat them that fast the speech cannot keep up with the speed of the battle, so you are basically waiting for up to a minute after the battle is over.
On the plus side, after the battle your wingmen have quite a few thoughts to share before attacking the SOLG. Break the game and you can easily listen to all of it rather than be interrupted by the attack if you went the long\hard way before.
The FALKEN's Tactical Laser System was brutal once you got your hands on it. Though requiring skill, it could instakill multiple fighters in one charge. You could even break the second half of the above final mission from AC5 with it - the aforementioned SOLG, a giant satellite falling to Earth, and with a single TLS shot you can literally cut it in half. The similar Orbital Satellite Laser from Ace Combat 3: Electrosphere arguably competed for the title of most overpowered weapon in the series because it could be used by any aircraft in the game. Though it's a Bragging Rights Reward because it's unlocked after getting A ranks on hard, a cheat exists where you can use it before having unlocked it.