It's better now in 2.6.3 than it was in 2.6.2. I still got a mix of ethics at game-start but in the 10 years before factions can form, the numbers had shifted enough so that only factions of my governing ethics formed. I'd designed my empire to promote my governing ethics, including making my species natural engineers to give some extra Materialist attraction. So at 2210 I had only an Egalitarian and Materialist faction. I had pops of other ethics, but no more than 2 or 3 per ethic. Then I did a bunch of deals with xenos and got enough Xenophile attraction that a faction of those formed. Now in 2260, I have no pops of any ethic other than Xenophile, Materialist, or Egalitarian. The percentages of those shift around a little bit.
My concern is when I start conquering I'm going to get factions form for other ethics and that will create enough attraction that I'll be stuck with them. It also seems that there is very little difference in how many pops you'll get of two different ethics once they both have any significant level of attraction. My empire should be about 50% Mat, and 25% of each other ethic, but in practice they all hover around a third each most of the time.
My concern is when I start conquering I'm going to get factions form for other ethics and that will create enough attraction that I'll be stuck with them. It also seems that there is very little difference in how many pops you'll get of two different ethics once they both have any significant level of attraction. My empire should be about 50% Mat, and 25% of each other ethic, but in practice they all hover around a third each most of the time.