Reporting in with my experience so far!
First game as the Banoserit on Normal difficulty. Challenging but fun, no serious massacres from the AI.
Second game however is turning out very different. Playing on Hard as the Ortain (Dictatorship). More challenging than the Banoserit but still fun. Went up against Ketarovs first, hit them early enough to have the advantage and wiped them out. Next were the Phaerax, who I had a tough time with for a while (especially invading their homeworld), but I eventually won.
The REAL challenge is my current conflict with a Kiadian Dictatorship. I'm getting absolutely destroyed by them; they're landing enormous armies on my colonies, not to mention their tech is miles ahead of mine. My hyperdrives are at 15k, theirs are 50k. My size 500-650 ships have ~150-200 firepower each (fighters), their size 800-900 ships have 500 firepower each! I think they have Plasma Torpedoes already. They're also packing a TON of armor (and probably repair bots too), as I'd have huge swarms of missile bombers focusing on one ship and it would still get away.
I know the Kiadians are good at research but man! This is crazy. And I haven't been neglecting research capacity or priorities at all.
I think I might lose this game.
Edit: Here's a video, pretty crazy! I had lost a lot of ships by this point but the result was the same even with 50 of mine vs 20 of theirs.
https://youtu.be/avx2-y7Scco