I have pondered that as well, which is why i am going for xenophilia so i can integrate/uplift races with desirable traits to make my empire run as efficiently as possible. But my own race is going to focus as hard on pure science as possible
Yeh. My point is that overall "Science heavy" builds will even out somewhat in terms of science with other governments, that do the opposite and up with 'geek aliens' to do science for them, and hyper effective X to give them room to build more labs.
I think it's far more important to center ethos and traits and even government on what you want your faction to be. Do you want your species to be run by a scientific committee - then yes, pick science directorate (though I think you may come to regret that, I've had to endure listening to a staff meeting at a faculty *shudder*).
However, you could also make a science heavy build with intelligent and natural sociologists species, which governed run by a moral democracy for the betterment of the galaxy. The extra happiness could mean that everything, including scientist POP tiles, works more efficiently, and internal peace means les resources spent on quelling rebellion and more is spent on SCIENCE.
Meanwhile, if you want your POP to be more standoffish yet scientific, you could create an xenophobic, materialistic, solitary, talented, natural physicists race, who decides to build their own android to keep them company, rather than having to deal with the foreign and disgusting biological xenos... or others of the same species :-(.
Eeh, the long and short of what I'm saying is "go with RP, not the highest
apparent science modifier".