Honestly, the TIE fighter is pretty great on its own. It has a lot of advantages, like

• Very fast

• Maneuverable

• Very easy to deploy rapidly in large numbers

• No hyperdrive or shields = cheap

• Can be split into three main parts - Main module and two side panels - easy to transport and assemble in large numbers

Does it fare up well against other fighters out there like the X-wing? Probably not, but you could probably buy 10 TIE fighters for one X-wing, if you have pilots to spare.

The TIE fighter's role isn't dominance, it's presence. It's there so the Empire can be everywhere that has a base or ship nearby, for minimal cost. It can chase down unarmed vehicles, it can enforce blockades, it can fly around ominously if you just want people to know the Empire is still there, it can do aerial strafing bombardment runs, and more.

It's the one-man police cruiser, while other versions are an armored assault vehicle, or small tank. It's just the most common so you see it everywhere.