I agree. I wasn't a fan of the extreme skeuomorphism that Scott Forstall introduced (iCal having stitched leather and ripped paper, for example), but overall the GUI was in a much better place then.

I bought a 2009 iMac with Snow Leopard on it and used it for the first time today, and found the process of finding, recognizing and clicking on buttons to be faster than in both Big Sur and even Catalina, despite me using Catalina daily. I don't have any data to substantiate this, but I think there's a good chance that interfaces with contrast, depth and well defined separation between elements are generally better suited to our eyes and brains.