I haven't used a direct image editor in a very long time and I don't think I'm missing anything.

Digital Fusion is free. Houdini Indie is $200. Nuke is available for linux. These are all node based work flows that don't destroy anything. You don't have to undo because you create a graph of operations without changing your source directly. They aren't useful for painting directly with a tablet, but anything else they do very well at.