Well, an update.
I returned the flat cutback. I rode in it four times, and it gave me back aches each time! I also felt like I wallowed around in it. I don't think my horse liked it either.
I decided to return it!
Then, I took my English stirrups and put them onto my Sycamore Creek saddle. This made it easily ten pounds lighter and made the cinch VERY easy to get to! Meanwhile, the things I'd always liked about my SC saddle--comfort, cradling, and leg position--remained in place. While I'd never be able to show in my new hybrid rig, it sure is meeting my needs and those of my horse!