There are plenty of good reasons to leave AS (network, product) but the frequent flier program is not one of them.
A mile flown = a mile earned, great partner award charts, and waived change fees for gold trumps everything else IMO.
If you fly 35k miles in economy as gold you earn enough miles for a free first class ticket to Asia on a top airline. That's 7 transcon RTs, which you can easily do for about $2000 (less if you are willing to fly saver on long hauls). To earn enough miles for a similar award on one of the "big 3" with similar status you would have to spend $10k - $15k in airfare. It's not remotely close.