I think part of the issue is that older free wheel cogs were a lot beefier as were the chains. New 9 speed stuff is thin and wears way more quickly. I just converted my XO-1 back into a 7 speed and I’m loving it. Feels really robust and I’m sure it won’t wear nearly as quickly as the 9 speed stuff I had on there.
If you’re touring and putting really hard miles on your bike it seems like 8 speed is about the biggest you want to go.