I wonder what Stellaris would be like if combat was more abstracted, and instead of watching two buckets of marbles scatter into each other, combat was all about managing masses of abstracted ships more in line with stuff like HOI, CK or EU, and was altogether secondary to the actual management of the Empire.
Cos I think when they make Stellaris II they should either make combat actually meaningful or else stop focusing on the superificality of smashing bricks together and more on the management of a nascent interstellar Empire
I've played games like that, and it tends to be very, very boring. Space 4X games tend to lean very heavily on the whole "research military tech, design your ships, watch them blow stuff up and be blown up in turn rather spectacularly" cycle because a lot of other concerns are absent. The concepts of terrain and geography are limited at best (usually not much more than hyperlanes/jump points/natural wormholes/limited life support range to create barriers and choke points, "this bit is in a nebula which means -50% to shields and sensors", and maybe something like Aurora where black hole systems will suck in and destroy ships with insufficiently powerful drives) because space is big, open, and empty in a way that really doesn't mesh with terrestrial grand-strat norms.
There's also the lack of established historical background and relationships that you'd have in other PDX games. You can see that they
tried to go the "develop history and galactic politics as the game progresses", but not really any more so than similar titles.
Basically, if you reduce ships and combat to "press factory to make bigger numbers, point pile of numbers at enemy numbers" you find yourself with a lackluster industry/logistics manager. Aurora aside, it's usually not terribly complex or difficult to manage.
Space 4X has a heavy focus on the exploration and combat elements because those are what it's best at. The space politics and nation-building is characteristically not that interesting and tends to exist largely to enable the former bits because that's the only reason anyone would care about it. The only way games in that vein like Neptune's Pride worked was by making it competitive multiplayer where every party involved was an absolute bastard of a human player trying to screw over every other player without getting dogpiled. GalCiv II pointed in the right direction by having AI that got harder with increased difficulty because the higher settings were clever strategists that would actively plan complex political strategies to secure different types of victory.
So yeah. Mainly lack of competition from dumb AI. There's no inherent challenge in smashing abstract doomstacks against AI that won't be as efficient at the macro game as you, so most of the fun is had in playing with ship designs and watching them shoot pretty lights.