So, how come no one complains about the jetpack being OP? Ten years later, and I still cannot stand this armor ability. How is the armor ability refueling IMMEDIATELY after you release the armor ability button not overpowered?! And it refuels pretty fast, I might add. It gives that specific player way too much freedom. Getting to certain areas of the map other players can't. You'll get slaughtered on maps like Uncaged and Pinnacle because of the jetpack. Explosives are obviously area of affect weapon. More than 90% of players jump before they use the rocket launcher or any other explosive. With grenades, grenade/rocket launcher and a jetpack, there is nothing stopping that player. Especially with TU. And these are the players that call armor lock "overpowered," simply because it helps us counter this trash gameplay style.
So, how come no one complains about the jetpack being OP? Ten years later, and I still cannot stand this armor ability. How is the armor ability refueling IMMEDIATELY after you release the armor ability button not overpowered?! And it refuels pretty fast, I might add. It gives that specific player way too much freedom. Getting to certain areas of the map other players can't. You'll get slaughtered on maps like Uncaged and Pinnacle because of the jetpack. Explosives are obviously area of affect weapon. More than 90% of players jump before they use the rocket launcher or any other explosive. With grenades, grenade/rocket launcher and a jetpack, there is nothing stopping that player. Especially with TU. And these are the players that call armor lock "overpowered," simply because it helps us counter this trash gameplay style.
Jet pack makes you a huge target across almost the whole map. I have yet to run into a player who destroys a team with a jet pack equipped. Just about all maps in MM have kill zones where they are needed to make sure they do not get where they are not supposed to.

If you are having a hard time countering them then start strafing. Its is extremely hard to aim left and right AND up and down while jet packing. I usually just start moving to one side continuously while shooting them and they can't make the third shot usually.
I've griped about the jetpack in the original and in MCC, but it's not going to change since it was like that in the original.
The jetpack is in no way overpowered. A DMR can easily take down a person using one.
The Jetpack is essential for FFA. On Penance, for instance, it allows swift and safe access from the Sniper Rifle straight to the Rocket Launcher. On Solitary, it does something similar and allows easy traversal of the map. Pinnacle and Uncaged are also places where the Jetpack is quite useful. It's pretty good for Sword Base, too. Honestly, Jetpack is the best ability for AR starts FFA.
On Penance, for instance, it allows swift and safe access from the Sniper Rifle straight to the Rocket Launcher. On Solitary, it does something similar and allows easy traversal of the map.
That's literally why the jetpack is an awful ability. It completely breaks the map design and power positions on the map. That being said, I think the only thing OP about it is the amount of activation time it has which was nerfed in H4.
So...I actually wouldn't call it OP. It has some decent Pros and Cons to it that balance it out.

---Pros---
  • It allows easy traversal over most obstacles on a map, allowing players to get from point A to point B quickly.
  • It gives players a better vantage point to make better use of explosive weapons like the Grenade Launcher, Rocket Launcher, or Concussion Rifle
  • It allows players to reach vantage points more easily to snipe, or allow for more creative flanking routes
  • It recharges quickly enough that a knowledgeable player can remain flying far longer then intended
---Cons---
  • You become a major target while you're flying in the air since there is rarely any form of cover
  • You lose mobility while flying in the air. It takes a lot longer to change your direction while jetpacking then it does on foot.
  • You lose accuracy. Aiming weapons like the Pistol or DMR is do-able, but becomes noticeably more difficult due to your own decreased mobility
  • Outside of trying to fly or fallout of view, you can't really use it to escape enemy players.
It makes you a sitting duck. Not OP at all.
Being an easy target is what makes the jetpack somewhat balanced, at least on the original Reach maps.
The Jetpack is essential for FFA. On Penance, for instance, it allows swift and safe access from the Sniper Rifle straight to the Rocket Launcher. On Solitary, it does something similar and allows easy traversal of the map. Pinnacle and Uncaged are also places where the Jetpack is quite useful. It's pretty good for Sword Base, too. Honestly, Jetpack is the best ability for AR starts FFA.
However, it kind of breaks almost every CE map, which were simply not designed for Reach. The vertical dynamics of these maps completely shift due to the jetpack, and I don't think it is for the better. Their weapon placement also becomes less relevant when using the jetpack because they become too easily available.