The dishback version is simply one of the many manufacturing options provided by CTS. They are mostly an aesthetic thing and are most popular for vintage style guitar wiring.
The dishbacks are supposed to have low friction, the flatbacks are high friction.
Pot quality has definitely decreased for CTS. I have metric CTS pots in my Coronet that are already scratchy after a year.
I have a Fender branded CTS pot in my Jazzmaster that is jiggly.
Same thing with the Switchcraft switch.
I've had better luck with Mojotone branded CTS pots but they have inconsistent friction. I bought two for my Coronet (500k dimple back split shaft) and they read 510k and 470k and only one is low friction enough to work well for volume swells