I was a happy NW camper (2MM happy), but I get fed up with NW well before merger. Hard to get upgrades on Int'l flights. Hard to get award tickets, etc.
IMHO the complaints about SM have nothing to do with NW. They are solely a function of the fact that DL has by far the worst FF program of any major U.S. carrier.
The only thing good about SM is the chutzpah behind the "Best in Class" claim and the fact that many people (including a lot posters on this forum) buy into it. PT Barnum must be chuckling in his grave.