Okay... so... you didn't plan for people to use the Tie fighters as a swarm.
More like "we didn't intend for people to be able to use TIE fighters in a giant blob that never suffers any penalty for sitting next to their powerful buff pilot". You can still take a swarm, you just have to think more about how you deploy and maneuver it instead of just throwing Howlrunner and a giant ball of TIEs in the general direction of the enemy and letting your superior math win the game.
It is obvious from looking at Howlrunner that FFG designed the Tie fighter to be strong in packs. This is the true nature of the ship. The Z95 is just another answer for a common Rebel encounter. Nothing is broken.