I can agree on a lot of what the OP said. But the things is, Stellaris allows you to take control. Use mods, mod some stuff yourself, play with some house rules or stick to a certain RP.
I usually play medium galaxies. Start a medium galaxy game, spiral, design some of the empires you want in the game, limit it to hyperlane, higher difficulty and you have a whole different game. I made my own mode to make the stations tougher because to me, it's insane that big 300+K fleets can enter a system but stations are tiny in comparison.
Really, a whole new type of game. Maybe it's because I used to play defensive end in football (and was D coördinator) and focus on D sometimes instead of offense.
You will allow the AI to gain ground (more so if you choose the right AI empires to be included in your game) making it tougher.
Don't reload the game if things go south is also a nice one.
And yes I do find Stellaris becomes partly boring after a while but only because I play it so much (1288 hrs) since the initial release.
That's an insane amount of time, at least to me. Insane.
But I always come back to it. Same as some Sid Meiers games like Colonization.
There is still a lot of work to do, but the community (mods) chances things up quite a bit. Try some of the AlphaAsh's mods, or total conversion mods.
If you still feel bored, restrain yourself from playing the game for 2 or 3 months (or longer) and then come back.
Try another game and see if it has the same vibe, style and potential of this game. Go play Colonization
