While Gimp has some UI issues, as someone who learned Gimp first, I don't "struggle" with it. It's very effective, and while you can call it a distant 2nd to Photoshop, anything else would be a distant 3rd to Gimp.

I don't do photoediting any more, but Gimp + plugins was great. In those days, it wasn't unusual for Gimp to get some new capability before Photoshop (e.g. Liquid Rescale, various denoising algorithms). The academics would often demonstrate their new algorithm using Gimp plugins.