Personally I diversify. It seems silly to me to remain loyal to one airline. None of the airlines have done much to earn that type of loyalty.

Having two airlines makes things much more flexible. Being 1k/diamond means that I can fly either *A or Skyteam and find an appropriately priced fare. When I am captive to one airline I find that my spend is actually much more inefficient. Amex travel has some killer J fares if you have a platinum card. often the premium economy is pretty inexpensive as well. AA often has massively inexpensive J fares to LHR which is a great way to jump to Europe.

Ultimately this whole status thing is foolish. They have people begging for scraps like an upgrade from CLE-JFK. Irrational behavior abounds when people think they will get something for nothing.