Chimeara

There is nothing the matter with the Chimaera itself (in fact, it still has a very strong kit, and much like Thrawn himself, probably the most ‘universal’ Capital ship when it comes to it’s supporting fleet).
Just look at the current geonosis TB, Chimaera and Hounds Tooth with a filler of of your worst ships can fairly reliably beat the combat missions in phases 2, 3, and 4.

What it is lacking is a synergized Empire fleet to support it right now.

Besides, it had it’s time on top - it was the dominant meta capital from it’s release all the way up until the next Legendary ship (Han’s Millenium Falcon) came along.

Power creep and faction cycling will likely eventually bring Empire fleets back around again someplace down the road.

If it's better than the Endurance, then it doesn't need improving.

Chimara was the best Capital ship before the last 2 was released and still is a good ship.

With it and 1 ship HT you can clear geo tb ship mission's by just hitting auto.