On France v Polynesia, I'm sure the 3 Gold of the post-Flight Chateau is no small benefit, and the 3 Culture Chateau at 3 per city will probably out-do a Polynesian city by game's end. But within the new BNW Continents script, I've had no problem getting +6 to +8 Culture from tiles in 3 cities by about T100 as Poly. And that's with planting cities on the coast and interrupting the line. Four tiles are easy to work in a size 8-10 city, and honestly the Happy, etc. from Policies are better for growth than the +1 food or any other option for that non-bonus tile.
That's really the touchpoint. If you think Culture is better at that stage you'll work that tile, and if you don't you won't. I don't see how any player is not working Moai's ASAP. Whatever guide is out there, maybe I'm even playing sub-optimally I don't know, but I find Piety an undeniably huge benefit as a second tree with CV, and that means a hybridized opening where you are chasing down your Growth/Happy policies along with one of the two work-able Reformations - Sacred Sites and Glory of God. Poly can do that, if desired. With France, it's just not available early. To beeline Chivalry after Edu, what's the cost and do you even get there in time to pick a Reformation when half the AI's open Piety? How many Chateau per city in the first place? How's your Worker budget enough even then to get them up quickly, considering your cities are full and ready to work the tiles otherwise?
Moais come earlier (by quite a bit,.. you're going construction pretty soon anyway whereas chivalry is probably post-education), and can clump... (chateaux cannot clump and by far I find that you end up sacrificing more valuable tiles such as flood plains to build the highest number of chateaux you can) played France in GotM and wasn't really impressed by chateaux; when early game and your satellites borders are still small, moais outdo chateaux by FAR in getting those borders out.
And trust me, that, + Sistine and early world fair win ends up usually in games where I never felt a single point of ideology pressure.
However, I would not go piety; even if Moai come sooner they still come too late (and you really need cargo ships to abuse them); you'd be better off at least taking the tradition opener.
I'm saying this again: Poly has something that France doesn't have: coastal bias and food cargo ships; it is very easy to send a satellite one ship and have it work 3-4 moai tiles even. Land routes are much less effective. 3 chateaux per city is not that much; 9 culture? 4 Moai in a line, not clump, (2,3,3,2) easily exceeds that amount.
Although, if terra is considered Polynesia definitely deserves ***, as that civ is simply amazing on terra.