Even when Vista came, people told all the time that they consider Windows 2000 to be much less UI-bloated than Windows XP; it was just that of the "UI bloat evils" Windows XP was considered to be the lesser evil than Windows Vista. I really heard nobody saying that XP was slim and fast.

BTW: Windows 7 is another story: at that time PC magazines wrote deep analyses how some performance issues in the user interface code of Windows Vista that made Vista feel "sluggish" were fixed in Windows 7.