I don't think you can blame the Kindle. I currently have 4 Kindle e-ink readers and a few Fires. I bought the Kindle Keyboard when it was first available and I've had every Kindle since except the ones without lights since lights became available. I've also bought quite a few of them for my neighbors. All are still in working order.
I have a case for when I take the Kindle elsewhere, which I rarely do. At home I use it without the case. I always have. Never a problem. These things are tough.
I guess if you'll feel comfortable with a different brand that can't hurt anything but the problem was your elbow, not the Kindle. Although you probably can't get a different brand of elbow.
Have you considered some sort of padding on your elbow for when you're reading?
Barry