I think ultimately, GalCiv provides a better "chess match" for players, while Stellaris provides a better "Role play experience".
The diplomacy system in Stellaris alone, whether it's meaningful or not, is far more robust and provides a lot of storytelling opportunities, then you have the end game content, fallen empires, etc.
IF Stellaris had had a ship editor akin to GC3, I probably would have favored Stellaris over GC3 originally... but since aesthetic ship design is my niche, GC3 captured my heart.
In a future GC title I'd really want a new map style... to allow for both on-main-screen battles and for choke points. I think the closest solution I've come to... is differentiating space tiles as "In System" and "Deep space". In system is obviously tiles around a star (or multiple stars) in a certain radius (and it should be a little random, not perfect spheres IMO) and use tactical engine speeds and are the tactical battle zones. Ships fight here, and can be stacks (just like now) but smaller stacks in general perhaps, and when a battle occurs you have a viewer window in one of your UI corners that is showing some nice animations in addition to the main screen (Dunno maybe works?). Alternate method is to copy Endless Legends tactical battles.
Deep space uses different engines, you can't fight on those tiles at all, and in general is much much slower than regular space to move through.
I think the result is that you have bubbles of star systems that act as strategic choke points, but they can still be maneuvered around strategically (but very slowly) and they provide a zone where tactical battles occur on the screen.
Additionally... tiles surrounding a planet would be "orbit" and a lot of ship stats penalized when fighting there unless they are very maneuverable and have thrusters.
Anywho... I look forward to StarDocks next venture into GC... but I kind of hope they just let GC3 end and get to work. LET US IMPORT OUR SHIPS THOUGH