Don't know if it's a myth or not. Some get by just fine ignoring the manufacturers recommendations and some have troubles getting engine replacements because of not following the recommendations.
My new bike had some limitations, under 7K for 200 miles, under 9K for four hundred miles, under 11K for four hundred miles, no full throttle for the first 600 miles. I adhered to those limits except for the no full throttle recommendation. This allowed me to get comfortable with the new bike and discover it's capabilities progressively. I certainly found new limits in handling and setup for corner entry during each advancement up the RPM scale.
I'm not saying that I'm right following the recommendations but I'm certainly not wrong.
This has been a shit show among the BMW folks.