I thought it was well established that AAs EXP was vastly superior to DL DM. I've read that so many times here that I thought it was a given...and I'm not disputing it. However, as Indufan points out, it's network, network, network! Not all of us can switch easily to AA. With my travel patterns, I doubt I could earn 100K on AA; although, I can easily earn many times that on DL.
Riding in front on coach fares is the most important bennie for me and Delta keeps me there consistently. Thus; for me, there is just no incentive to switch...best-in-class or not. For those of you who can switch and believe that doing so is best for you, I encourage you to do it and don't look back.