This isn't a particularly strong or meaningful argument for GTS or PD.
1) Forza Motorsport 6 didn't have dynamic day/night or weather, but rather it was "baked" into the environment, so it was only an option where they actually rendered it. They've been anal about not sacrificing performance for the sake of cramming something extra in. Games like Project CARS did some neat stuff but at the expense of performance. Turn 10 insists on 60 FPS locked, and won't settle for any dips, not even accepting a drop of just a few frames. CARS, on the other hand, was all over, and I've seen it look like a flip book on several occasions.
FM6 was their 2015 game. They now have FM7 coming this fall. That's a better, more fair comparison for GTS.
2) As for outsourcing, that's not really relevant. They pay for what's produced for the game, whether it's developed in-house at the expense of paying their own team for that labor, or if they pay another team for the same labor. They use whatever resources it takes to get the job done. If PD need more bodies, they can employ them, whether hiring them in-house or hiring a third-party.
.
