There is nothing wrong with the user manual
I used to break in new racebikes. The chief engineer instructed me to be gentle until normal operating temp was reached. Then increase rpm 500 rounds every few minutes while accelerating and increase the throttle as well. If all goes fine, accelerate a few times at max power.
Meanwhile, do the same with tires, brakes etc.: increase the load after normal op temp reached.
Then let it cool to normal temp while cruising, stop and let it cool completely: done.
These engines never blew nor extra oil or fuel.
The whole procedure takes 100 kms.
I think it takes a normal driver more miles to get used to the car, get eveything through it cycle etc. If you break in on purpose, less miles will suffice.