I'm a long-time DT user. I've tried GIMP and wasn't in love with it. If memory serves, it had a lot of the old Broderbund Print Shop feel to it due to the features. I also tried it with DT as a plug in and wasn't thrilled. Having said that, it could've just been my inexperience with GIMP, I know a lot of people use it and it's popular.
I separate post into two categories: Processing, which is Darktable's (and other programs of its ilk) focus, and Editing, like Photo Shop and Gimp. 99% of what I do is processing, but if I want to get deep into editing like layers, I use Affinity or Paint.net.
HUH? PAINT.net? Yup. Originally conceived by MS as an upgrade to Paint, it was ultimately abandoned. The main designer turned it into an open source project. It's free, well supported, and pretty versatile. It won't open RAW, but if you want a free editor that looks very familiar (think Windows) and is user-friendly with a very shallow learning curve, it's a good option.