Windows 7 was not that fundamentally different, but by the time it came out the bandaid had been ripped off.
Windows 7 was in many aspects Vista SE, they just had to give it a new name because Vista was so „tainted“.
I mean it even reported as Windows NT 6.1 (Vista was 6.0)
The first could have been easily avoided, but I genuinely don't know how MS could have avoided burning a version on UAC. Maybe if they had shipped it in a service pack first so that XP SP4 was the thing that got a miserable reputation? That clearly wasn't a reasonable option after the Longhorn disaster, though.
There were also a lot of small problems that got fixed on the way to Windows 7. 7 did feel a lot like Vista SP2 with some visual tweaks, but it would have been a really impressive SP.