I've steered away from using Hab's on worlds I don't plan on Terraforming if at all possible, due to the pop auto building infra and moving to the surface and causing worker shortages because my Hab peeps now have to work extra hard to support the idiots on the planet.
As Jorgen mentioned and you implied by your quest to find a better way - Unless it's for Role Play it's a pretty straight forward formula. Is the bonus worth the cost. Since it's not given, I'll assume 100% bonus for now. Your choices seem to be try to just get the 10M (iirc) in orbit for the empire wide bonus, or staff 30 labs to get a bonus 30 labs of RP. Seems a lot of effort unless your current pop is a bottleneck for 30 labs worth of RP.
I think the 'idiots on the planet' (whom I also hate) pay their own bills, labor wise. It seems to be tracked separately from when I was dealing with that (though I could be wrong).
This was my understanding. OrbHab population is supposed to be exclusively manufacturing, and the pop growth + infra that propagates down to the planet surface is purely extra on top of that which is subject to the usual rules - in which case it's free infra, so...
That's what I thought too, but I haven't had an opportunity to do it in a real game. I just tried it out though, and found that this is not how it works.
I've tweaked the environmental tolerances of the humans in my current game, so Venus has a colony cost of 50. I SM'd in an orbital habitat and a million people to live in it. 0.82m went into the manufacturing sector, 0.18m into services, and none into agriculture as expected. So far so good, although I would prefer if a fixed 5% of people went into agriculture, even if what they're really doing is making spare parts for the hydroponics gardens.
Then I added 5000 infrastructure and another 1m people. All one million of the new people went into agriculture as expected for a colony cost of 50, but now there are only 0.58m people in manufacturing, because so many people have shifted over to services.
Adding another million people living in infrastructure brings the manufacturing sector down to just 0.3 million.
So it seems that you do have to keep up with population growth by continually adding more orbital habitats in order to maintain your manufacturing sector population. If the planet has a large natural capacity, that will add up to a lot of habitats that you'll have to build and move into place.
I don't recall if any of Steve's games have involved using orbital habitats to staff labs on a body with an ancient construct or not, but maybe we should ask him to SM one in on Venus in his current game and try it out. It would be interesting to see how often he needs to send a new habitat to maintain the manufacturing sector, once he can set it as a stable population.