To be fair they're not hiding it. There's a link to imaginAIry in the footer, even on the pricing page.
Are you using the word "just" in a dismissive manner?
To me, "just a wrapper" makes it sound like it's something completely trivial but I'm an experienced web dev and I wouldn't even know where to start. How do I run this stuff on the server and how do I expose it in a web UI like this?
RealESRGAN is available as a command line tool you can run on a gaming PC. So you'd build a site that does image uploads and a worker process that upscales the images. That hardest parts are off the shelf open source libraries.
I'm increasing the workers, didn't expect this growth
That's great. You already know this but ignore the people trivializing it. Yes, we hackers could get this running without much effort but most people are not hackers and have absolutely no clue where to start. Even as a hacker there are occasional tools that I don't have on my system at that moment so I'm very thankful to have easy point and click websites people have built around the tools, because it saves a ton of time. Time is incredibly valuable to me now, and I'm happy to pay for things that help me do things faster.