Photoshop is the de rigueur because it was one of the first to be accepted by the artsy/film/advertising folks and became mainstream for what it does. Adobe had a huge momentum and as usual, once you get accustomed to an interface, you stick with it. PS is one of the programs that made the Mac so popular among artists (and still is, though the gap isn't what it once was). And if you're the type that is making money with the software, you'll continue to buy because you can recoup your investment. Not so much as a hobbyist. I've had Photoshop since v2.0 (came free on my comp) and got a discounted v3 so many years ago. I don't upgrade regularly and stick with a version for a long time, basically until my comp wouldn't play nice with it anymore. That said, I'm holding with CS6 because I too dislike the subscription model. If you do the math, and upgrade as each new version came out, the subscription model comes out cheaper $$ than upgrading (typically, an upgrade was over $200 each time). But that's only if you upgrade regularly. For someone like me (hobbyist), it doesn't make sense either way, so I just hold old versions until I can't anymore.
PS was created by Thomas Knoll while a grad student at Michigan, calling it Display and later, Image Pro (which was taken) then subsequently Photoshop.
There are MANY alternates to Photoshop. What PS had originally (and mostly still) is that it can give files ready for print (CMYK) and had max print capability (as well as total integration with Illustrator, the vector creation software). Unless you're a professional, you don't even need this capability. Plus, it was one of few programs that had layer capability (was a HUGE breakthrough in the day as EVERY change/addition/edit could be overlaid and adjusted independent of the bottom layers, etc) at the time. Now, many have this ability. If you google, you'll see there's a FREE copy of a program called GIMP. It's an open source emulator of PS. It'll do just about everything PS can do. The catch is, you have to unlearn the PS interface a bit and get used to the new one. As is the case with EVERY copycat/emulator. And most, once they get used to something, it's less than ideal to learn new habits. We like what we like and don't want it to change, hardly at all. My wife likes to do graphics too and fought this idea when Paintshop Pro went old along with her PC and I 'Mac-inized' her (mostly because fixing PC issues made me prematurely gray) compared to Mac issues.
There's quite a few alternatives now that are not as expensive. GIMP, Pixelmator, Corel Paint, Corel Paintshop Pro, Paint, Acorn, Seashore. Which are all raster programs as opposed to vector art (imo, a bit harder to use).
And a lot of the dedicated photo apps also include some PS abilities when adjusting photos.
JB; I found your adjustments could have gone further in that you can pull out the medium gray shades more/better in the two examples you posted, using the middle slider in the Levels dialog. (course, it may be my monitor--as of the moment, my tv, that is showing this darkness, but since the blacks and whites look fine, I figure the middle grays just need more tweaking). I'm attaching my simple try at the above; please don't take offense and yes, I know ALL art is subjective. Just pointing out how to pull shadows out from under exposure.
For most folks, PS type programs are overkill since most just want to 'fix' their photos and there's more than a few software programs that'll help you do that. Though, I still use PS for a lot of that as I've gotten used to it first. A lot of folks used LightRoom, and are also now wailing because Adobe has gone subscription with that, too.
Adobe makes good software but many are looking for alternatives, whether for cost consideration or standalone/subscription ideals. Professionals though, will stick with what has worked, at any price. It's only us hobbyists that have to keep up and adjust with the times, usually changing and altering our programs to fit our need.
Michael
