I will be the first to 100% agree with that being I have 'butchered' so many things on bikes and cars to have them in no way be called OEM any longer. Can't count actually.
The early DOHC specs for valve clearances are a perfect 'stick it in your eye' example of wrong headed there. The torque spec for the cam caps are more of the same-WRONG. And cam clearances in the caps going from 3 on the outer to 5 then to 8 on the inner? What could they possibly have been thinking there? That's just all around goofy.
The main reason though I push the OEMs is that at least in the not so distant past many also added detail to explanation of how things actually worked to vastly improve rookie knowledge if you are one to 'pick up the books'. Now though, the reduction in overall worker pay and the necessary dropping of so many A mechanics that began in the '90s to now rely on mainly B's and C's to increase shop profits has turned the service manuals into nothing more than glorified flow charts with steps by the thousands, they simply tell you change the part or go to the next step and worker still has not a clue as to WHY at all. If you can't figure out exactly what is happening in the flowchart you are lost. With all the thousands of pages of multiple step flows they have no more room for the explanations any longer and it doesn't matter to them anyway as that only makes the employee smarter as in smart enough now to know he needs a raise and getting screwed there.
Making many service manuals now virtually worthless, or like the '12 Nissan one I just got, you have to search forever through flowchart bullsh-t to then find the 5 pages out of every hundred you actually need. I'm surprised the modern attention deficient worker is not snoozing by the time he finds his flowchart. Me, I don't care, I can cut through the crap there like lightning to find what I need lickety-split.
Just like everywhere else in this great land we are looking at the total dumbing down of the working class even further to be able to get a JOB..............as if a minimum wage 'world class' job is going to do you any good at all.
Luckily most of us here are still working on early bikes and those manuals are MUCH better.................