You can't go wrong following the owner's manual! Engineers with decades of experience designing and building motorcycle engines and transmissions probably know better than some yahoo on the interwebs.
The famous website recommending break in by running hard is a racer. He has anecdotal evidence at best regarding engine survival over a few races under race conditions. Most of us don't run our bikes like that, and we're looking for decades of reliable mundane performance. He discusses piston ring seating but he doesn't discuss other important engine parts like camshafts or valves. There are many surfaces other than cylinder walls.
In aircraft piston engines the break in consists of high power but low rpm for a few hours. This is to seat the piston rings. Oil consumption can be higher than normal without doing this. So, my opinion is that the motorhead guy's break in does a similar thing, imposing high cylinder pressures which encourage proper piston ring seating. But, he does it at high rpm which is probably harmful to all the other mating surfaces which are not yet polished into each other.
A lower rpm high throttle motorcycle break in may have some merit compared to lower rpm low throttle, and in fact the owner's manual does not prohibit it. Normal riding, though, is difficult that way unless you drag your brakes. I would be shocked if the engineers did not consider piston ring/cylinder wall break in when they developed their recommendations. For some reason, low rpm considerations won out over the balls-to-the-wall break in method.