I use Photoshop alternatives because they're cheaper than maintaining a perpetual license/subscription, but Photoshop is the big gorilla because it is the best photo editing app in the industry today. Bar none. And that's what lets them get away with their pricing structure.
Nobody would pay for Photoshop if it didn't provide value.
I am (1) a current Photoshop CC subscriber and (2) an owner of the second-to-last version of Photoshop that was available under a perpetual license, and I disagree that Photoshop is the best photo editing app in the industry today.
For photo retouching, I prefer Affinity Photo. One thing I especially appreciate about it is how efficient it is at handling large, 16-bit-per-channel images with many layers.
Photoshop is useful to have around mainly because it makes it somewhat easier to work with certain kinds of PSD files that I get from other people.
I also have Photoshop CC and Affinity Photo, and while I use AP for the simple stuff, it can't hold a candle to the more advanced stuff you can do in Photoshop that is still on the (long-term) plan for AP.
Nobody would pay for Photoshop if it didn't provide value.