Some of Aretha's singing was used later in the series we saw. The end was great. She filled in for the ailing Pavarotti. Aretha was no opera singer; however, I think it worked because she felt the aria, and the audience was mesmerized. I agree that it would've been great if those songs were included. Maybe the writers wanted to show more of her range and catalog, or perhaps the actresses playing her would have to fake it to the point of the lip-syncing being obvious?
Jennifer Hudson is great in her own right, and she looks a bit more like Aretha. Will we see the true story though. Probably not because it's on Lifetime, and there'll most likely be much melodrama about her tumor surgeries and subsequent death.
I remember seeing Aretha's last show on PBS in which she looked very thin and frail. The audience gasped when she walked onstage before applauding. Anticipating that, she sat down at the piano in her flowing white gown and said "I've finally lost the weight," and began to play.