If a "hub" airport is such a factor, consider this:

Why is WN flying into LAX? LAX is notorious for delays and is a busier facility than SFO. Between SFO and LAX, I am sure that those airports cause a lot of grief to WN for their on-time performance. Fortunately for WN, they do not have a lot of flights into SFO. When I fly into the Bay Area on WN, I always go through OAK. It is always an easier and painless BART ride into The City from there. Also, I really like going through OAK...less hassles.