Hi MOC,
your request was to maximize miles within OW.
JFK-GRU
a)AA951 direct or
b)via Miami where AA flies direct or through a code-share with TAM . You'll get your boarding ticket under a AA7661 or AA 7663 and Status Miles both cases. TAM is excellent.
b) GRU-EZE
You may get miles (not Status) both with TAM or Aerolineas Argentinas direct flights. If I were you I would certainly fly TAM. Their service is outstanding.
Lanchile (OW) would be a mileage run and expensive. I would not recommend.
c) EZE-MEX
Being OW then its EZE-MIA-MEX with AA or EZE-SCL-MEX with LanChile, both will get you Status Miles. If you were Star Alliance then the option you mentioned EZE-GRU-MEX with Varig would be proper.
d) MEX-JFK
You can do it with AA through Miami or DFW and earning Status Miles. Direct Flights only through Star Aliance.
Have a nice flight !