After having been gone for a while myself and having played a game. Here are the big changes I noticed.
-Psionic leaders got buffed massively, it used to be the leader traits for psionics were kind of mediocre. No more, they are easily one of the strongest now.
- Cyborgs, likewise, got nerfed hard and repeatedly. Not only are the leader traits now mediocre, but cyborgs also have the added penalty that they cannot benefit from brain slugs, if you get that event. Not sure why, cyborgs still have fleshy bits in them. The species trait is still the same, but the meta shifted, habitability is no longer as substantial as it was.
- Bio ascension is mostly unchanged, but Erudite now has its own leader traits, unfortunately those leader traits are even worse than cyborgs. Bio ascension's newfound power is largely from the meta shifting than any specific changes.
Now, synths.
Robots in general have undergone some massive changes. In the days of old, all robot pops can work all jobs, but they had various resource penalties and bonuses. Synths were famous because of their +20% production bonus to everything. However, all of those bonuses are gone, and the only differentiation between the robot types is what jobs they can and cannot work. Now, you can mod robots like organics, and robots have traits of their own. On top of this, non-AI robots (under Outlawed AI) consume 50% less housing, 50% less amenities, and 100% less consumer goods.
Between all those changes, the meta practically flipped on its head. Free synths are now mediocre, especially since they cannot get the research/unity production they used to be able to get (there is no research bonus/unity trait for robots), while properly modded non-sapient robots can work your technician, farming and mining jobs because there are traits that provide 15% bonus to those. Non-sapient robots also consume 50% less housing, 50% less amenities, and 100% less consumer goods which means you can pack a lot of them on a planet, which makes it almost trivial to unlock the 70 pop requirement for all buildings on even small planets.
Now.. in light of all that, synthetic ascension is just not very good anymore, since most advantages have been cut out from it and its disadvantages are still there. There is still the habitability but, habitability is no longer as big a deal as it used to be.