Check out Scribus. I'd describe it as more of a serious publishing app, where Inkscape may be more for artists. Scribus uses less resources and supports multipage documents.
I've also had issues with the cage transform in Gimp, but it's fixed now, so if you're on Ubuntu, just add a PPA with the latest version of Gimp.
> 1. a good raster photo editor with non-destructive editing capabilities
I think Darktable does non-desctructive editing but I haven't used it myself.
> Gimp and Inkscape are both extremely sub-par apps... Paint.NET beats Gimp in usability, Photoshop in both features and stability.
I think it's a bit sad to be whinging at those good pieces of free software for lacking features, and just recommend proprietary software instead. Surely, it is also the developers of the proprietary software that are causing this lack of features by not sharing their code for those.
It also suggests you are willing to give up your freedom for a few extra features. What are those features missing in Gimp? (Gimp does have CMYK editing, if you install the gimp-plugin-registry package.)
> Linux desktop desperately needs:
Those non-free programs you mentioned can probably be run with Wine on GNU/Linux.