Agreed. I've seen there is a mod to add more mid/late game encounters or content, but I haven't tried it yet. I think more developed diplomatic events would make mid/late game more interesting. Most of my playthroughs end up being an arms race towards the end, which sure that can be a fun aspect of the game, but not super interesting. Very much like civ, and I think you're correct they both suffer from the late game "domination" aspect.

My idea of a successful Stellaris game it not coming in first, but making it to the end with a functional empire.

I'm also probably a noob when it comes to Stellaris, but I still enjoy it.