There's a reason the only 3-HP ship to see regular competitive use is the TIE Fighter.There's a reason the only 3 agility ship to see regular competitive use is the Tie-Fighter.
That's what you meant to say there, or at least what you should have said.
The 3-agility ships aren't touchy in competitive play because they rely on agility - they're touchy because they rely entirely on agility. They have no shields and very little overall life, meaning that even a slightly bad die roll is very bad news, and a moderately bad roll can be catastrophic. The Defender does not have this problem. A TIE Fighter or Interceptor can potentially die in 2 uncanceled hits, with the right crit. The Defender requires a minimum of 5. That's a rather massive difference.
And yes, this is a game based on positioning. But the Defender isn't good at that. Turns are incredibly important. Especially 2 turns. With the linear nature of the defenders dial it's named pilots are going to suffer from being blocked.
The balance issue here is how similar the Defender is to a Firespray, which is among the best ships in the game. The Firespray's rear arc isn't as good as a White K-turn, but it has more uses. Being able to take a 90 degree turn andand fire behind me is amazing. Crew slots are also amazing.
If it had something to offer that truly made it different from the Firespray, say Boost, or sensor upgrade, it would be an equivalent ship. But just having a small base doesn't cut it. Barrel roll is good, but works best combined with turns, boosts, cheap swarm ships, Sensor slots, and large base ships.(Silly as it feels) It doesn't feel right on the defender.