I HAVENT DONE THE MATH
But I checked out my saves and started a fast new one for the last hour, been trying to figure out is it really that important.
The short answer is YES it is quite important but this doesn't mean that this is a bad thing.
First of all, there are few thought processes we need to alter with the 3.0
It's ok to leave building slots open during the early game.
For a quiet while players had to build something new as soon as they reached a certain pop count. Now the pop count doesn't really matter for buildings, at least in the mid-late game. During the early game, yes, it is frustrating to see so many jobs open; that doesn't mean it's going to stay that long.
Research is still the king!
Having dedicated research planets are quite influential (as before) but since every pop is more valuable than before, you would definitely want to improve to the better buildings ASAP
POP specialization is further buffed
Before...The quantity of the pop was important; that was the way to build. Now, you can always build the infrastructure way ahead at the same time creating unique species or robots is now quite important. There is no tolerance for the "trash population" anymore. But having several types of species with the desired traits are quite powerful now. It's a neglectable penalty (-10% specific species) when selecting the desired pop type; quality is more important now.
Machines are quite OP now
It seems to me they don't get affected by this max population cap. Which is quite a buff and means they could always steady population production.
Having said all of that, to me, this newly introduced population race isn't that of a big deal.
You can still get quite buffs to your growth value even though the required number is always increasing. The race favors the growth value if you focus on your research.
The migration bonuses are way more beneficial now, not to mention they give more bonuses for what they take away from you ( the balance of emigration/immigration favors immigration)
Slavers, and such... who plays with lots of population need to go and actually conquer because they won't gain pop steadily and slaves also, so it forces them to go for a hunt and balances them a bid.
Overall I would like to see some maths regarding the immigration balance of things but I really don't see a "huge" issue here. Maybe they could slightly balance the ratio just to please the players.