Vista was Longhorn redone with COM instead of .NET, after the whole internal drama from pro C++ folks, after Sinofsky took over.
Window 8 was .NET redone by the same folks, as the original idea from Ext-VOS, COM getting IInspectable, in addition to IUnknown, while Type Libraries replaced by .NET metadata.
Windows 10 was the reunification of WinRT programming models across devices.
While yes they did introduce GUI changes they also introduced a lot more fundamental changes. Typically the second release is seen as better because it's usually a refined version or at least the changes had more time to perculate.
For example Vista introduced many things that changed the fundamental nature of Windows, UAC (split tokens, integrity levels, etc), new audio stack, overhaul of IPv6, new display driver model. A lot of these new driver changes and the extra hardware requirements caused a lot of issues whereas when 7 came out the requirements were no longer as burdomsome and manufacturers had more time to release better drivers.
Windows 8 introduced UWP silos, new startup process, Hyper-V as a client. 8.1 and 10 were definitely more iterations on the GUI and other features to make it a bit more palatable.
There were massive changes in Vista, new audio stack, new default permissions, new USB stack, new networking stack, new graphics stack, which caused tons of compatibility problems.
I may be wrong in some of the specifics, but the truth still is that every other version is half-baked OS changes with the main selling point to consumers being the upgraded GUI changes, while the actual working OS comes as the next version.
Vista was essentially XP with the GUI for Windows 7, Windows 8 was essentially the Windows 10 GUI with the Windows 7 OS, etc.
11 is just 10 with broken GUI updates, 12 will be the finalized version of the 11 GUI with the actual underlying OS updated as well.