This actually brings to mind: I used to work with a guy who had a strong background in cycling. He was multiple times national champion in more than one discipline, and lived and breathed cycling in every way.

He told me he was quite disappointed with the way in which 9 sprocket cassettes and their derailleurs worked, when Shimano replaced their 8 speeds with 9's. He stated that the rear derailleurs felt less precise, and that he would have liked to keep riding an 8.

My first ever "real" mountain bike had the 8-speed XT cassette at the rear, and an XT derailleur and shifter. I must admit, "upgrading" to a 9 speed felt like a downgrade in shifting precision.

Having said that, even with the 8, there were slushy days where the cassette was just packed with so much stuff it was a real shit show.