AC is critical here in Florida and I can tell you that the new refrigerant requires much more pressure to operate and is far more prone to leaking ... The components used have to be the highest quality to last any respectable amount of time in use,, I don’t know if Mexican production can do it reliably.
You are correct in that AC requires top notch assembly. Materials will probably be brought in from outside Mexico, but the welding of the piping, etc. for leak-free is not easy. If they move to Mexico, it will take some time for them to achieve their original American standard of quality.
My AC guy hates the new units. They break down so frequently he ends hip with a lot of warranty work that is far less profitable than installs, repairs or routine servicing.