Maybe it’s differing expectations, but I’ve been happy with the EU4 AI and feel it’s quite good as far as strategy games go. I’m not just referring to it’s performance/competitiveness, but the game provides a lot of interesting systems for you to interact with the AI. The way alliances form and fall apart feels a lot more organic than other strategy games. You might be natural allies due to a shared rival and that alliance might last a century, but once you start competing over the same strategic objectives then they often fall apart. The fact that the AI works in a consistent manner where this can play out in a more believable/organic manner is pretty impressive, IMO.
Stellaris AI has always been at the bottom of the heap, unfortunately. It’s another victim of the massive overhauls the game has seen, IMO. I have to imagine the economic AI had to be rewritten from scratch with MegaCorp and that has impacts throughout the game. And teaching the AI to design competitive ships is tough in a game where the meta shifts from patch to patch, often in unpredictable ways.