Last I checked GIMP had some limitations that limits its use by professionals. There is no support for PANTONE® colors, which are encumbered with intellectual property claims. Specifying colors by PANTONE® code is pretty crucial for print work. There is also no native support for the CMYK color model.
Most people who post on forums like this saying there is no difference between GIMP and Photoshop probably have only used these programs to create or edit electronic images. The print world is a whole 'nother ballgame.
Like the OP, I find the new differentiation in the File menu between Save (meaning .xcf) and Export (everything else) annoying. It is inconsistent with most GUI designs where the filetype determines the format as was the method in 2.6. I really don't see the value in changing it. I also liked having a tool's options open automatically in the lower half of the toolbox. Now there's a message about drag-and-drop there, but I cannot get it to work for me. If I double-click a tool, it opens the options in a separate window. I've tried dragging that window onto the toolbar to no avail. If anyone has a quick answer to this, I'd appreciate it. Otherwise I'll do some research.
I think I might compile v 2.6 in /usr/local, so I can run both versions.
Edit: Not as easy as it looks. I've again encountered versioning problems with GEGL.