Pretty much all movements for watches under $8000 are all mass produced by precision robots in a highly automated way. Personally, I prefer gen Omegas and gen IWCs because they take highly proven movements and upgrade them even further to make them even better. A top grade ETA 2892-A2 can hang with a Rolex 3135 in terms of durability, accuracy, and stability. Now take that top grade and finish it even better (it's already finished better than a Rolex before upgrades) and add a few more jewels to some areas and you have something even more amazing.
I personally don't get the reasoning why you wouldn't want a better than top grade ETA movement over something that's "in house" which is really a sort of superfluous term since quite a few "in house" were designed elsewhere and purchased or even made elsewhere.
The 8500 is made 100% by ETA and was designed by teams from all of Swatch's top brands. When Omega's new facility opens, it'll be produced exclusively there by Omega and only for Omega. It's an incredible movement.