I see, I haven't played much since machine age dropped so I didn't realize modularity pop assembly was that crazy.Without Polymelic or Budding, Genetic can't beat Modularity (or even Synths) now, though both of those need to pay a small pop tax on assembly.
Genetic gets Exotic Metabolism, Fertile, +20% from techs (7.875 growth) and Vats plus Vat Grown (5.625), for a total of 13.5
Machines get Mass Produced, Monoform, 4 Roboticists (with 50% extra base output) plus a Synth ruler, and 20% from techs (plus another 20% from Rapid Replicators, though it's probably not fair to count that). (4*2*1.5+1)*1.45*1.2=21.06. If they really wanted growth they could also grow organic pops for another 5.85, but those pops won't get their absurd +60% output from Dark Matter Engines, so they probably won't want that.
Even with Vat Grown and Polymelic, genetic would need 120 pops per planet to match Modularity's growth. And if Genetic gets Polymelic, then Modularity gets the scavenger bot trait (another 50% growth that's additive with the other two traits).
They also both have agendas and a few council positions or civics which boost assembly/growth, but those are temporary so it gets weird.
I've probably forgotten something genetic gets (don't have a save in 3.12), but 13.5 vs. 21.06 (with another 5.85 if you really want it) is a very wide gap.
Unfortunately it seems we have to wait until next year before genetic or psionic get the machine age treatment.