Used oil analysis is certainly definitive. But it's like a "cause of death" indicator, if you are actually having problems. And there are many different type of used oil analysis. What info are you looking for? Would you know what to do with it if you got it?
Who has the resources to have their used oil analyzed every time their oil gets changed? If you do, then good on ya... you're certainly in an infinitesimally small minority. For those that can't - or won't - be bothered... there are literally millions of road vehicles that have average owners that change their engine oil on the schedule recommended by the manufacturer... both of the oil and the engine... there's a reason for that, and you don't see oil-related engine failures because of that simple fact.
And ya, manuals are written with input from engineers. Of course they are.
Bob is not the oil guy. Bob is an oil guy. And unless Bob is your oil guy, and he's paying for your maintenance on your bike, take his word - and the word of contributors to his site - with a grain of salt. Do your own research, until you understand the subject. Your use of your engine in your area is unique. There's some good info on his site, but it isn't all absolutely true.
Do what the manufacturer says, and you'll statistically be with the majority of people doing what is safe and right for your engine! If you are doing something like severe dirty/dusty/cold/hot service, or racing, or something else not covered by the recommendations in the manual for an average user, then change more often! Use synthetic! No requirement for used engine oil analysis for the average user. But hey, you got the time and the cash and the smarts, go for it.