The problem is all the WP themes I’ve looked at that purport to be minimalist and simple are anything but. The main criticism being the instability of the interface. Things are forever flying around the screen, including even navigation menus! The other criticism is that they often unnecessarily complicate the WP admin with their own complicated gallery interface, instead of the native one.
Are there any simple WP themes out there like these, with a consistent stable interface?
custom WP theme
Your issue is that these are not good enough or up to standard for sale here (that’s kind of often the difference between premium stock marketplaces .v. custom builds).
If all you want is a basic theme with WP interface then you probably don’t need a premium theme - an of the free ones would do it and a gallery is default functionality.
This guy keeps a lot of their files simple as does here or here or here and if you want awesome flexibility (you just have to pick and choose the best features) here.
There are many but those spring to mind and there’s nothing stopping you removing the necessary stuff you don’t need in any theme - that way you get the value of premium level themes without needing to use any overly creative features.
+1 for the themes by @ThemeBeans - they are great fun to work with and stay very minimal / clean / simple / no-bloat.