mythical “average casual user”
Mythical? You realize people like this exist, right? This is why programs like this exist. Take Audacity for example, it was made with non-professional audio people in mind. Just people who have odds and ends to do with audio. It’s simple enough that someone with no prior knowledge can start poking around and figuring things out, and it’s advanced enough that it can get the job done for most people who need to work with audio files.
I’m not saying that GIMP needs to prioritize the first time user experience. If making the UI/UX more approachable for new users would necessarily make it worse for established users, then it may be a decent tradeoff. Denying the existence of people who just need to edit an image here and there is absurd though.
I think I could get by with Bitwarden/uBlock as a minimum. Addons like enhancer for youtube are super nice though.