Steve,
I agree with a lot of your post but Timothy B. Schmit's band POCO before he joined the Eagles have a legitimate claim to the origin of the Southwestern Rock (sometimes now referred to as classic country rock) sound. Maybe splitting hairs a tad since Tim's contribution is huge in both groups but POCO had a few years headstart. Never quite made the real big money but Tim and the boys did all right for themselves. Check his website for some fun backstory.
http://www.timothybschmit.com/
Bill
