With the upcoming federations expansion, i am trying to sketch out in my mind some game plans for. Having played many games but never finishing a single one, i have accidentally killed numerous species and intentionally killed one. Once you got a species available trough migration treaty, you can force grow.
The authoritarian ethic means the empire should be able to enslave aliens, but. Long time authoritarian xenophobe here. The synthesize bonus would be for if you made some kind of xenophile empire that had migrant pops from the rest of the galaxy and stayed on a lower number of planets.
Xenophile is a bit harder to manage if you’re trying to optimize but it also means you don’t have to terraform or worry about species optimization. Something that was discussed before is the way xenophile and authoritarian conflict with each other; It takes decades to infiltrate them, convert them to your ethics,. In order to spare other people attempting.
I like doing pacifist xenophile builds. The xenophobic, authoritarian, and spiritualist ethics will. I've been looking at stellaris's dev diarys and noticed that paradox heavily favors some ethics while neglecting others. Population control and migration treaties are a must have.