I get 13K miles out of a set of Bridgestone Exedra Max tires. The OEM Metz are lousy when it comes to long miles.
The only drive shaft issues I have heard of are fixed by proper grease at every tire change. Those who do not but the proper amount of MolyB on the splines will eventually get a lot of rust there.
Most of the transmission issues are on the first group of bikes. Triumph issued a fix it kit back in the day and have since corrected the issue on bikes at least back to 2008 as far as I recall.
The detent spring does break on some bikes. It is an involved fix but evidently not that hard if you have a wrench skill and proper tools.
My clutch went our around 57K miles, and I have had a number of switch issues due to water or corrosion. Keep in mind I do not have a garage and the bike sleeps under a cover year round. And I ride it year round too in all sort of bad weather. And on top of that, I am notoriously known to not clean my bike except when it rains...