I agree with hard engine break-in. It was instilled in me as a young child by a well known aircraft engine builder where I grew up. We would rebuild continental, lycombing, and Radial Pratt engine. (I was the helper). We would perform a run up on the dock ramp, do all the checks, once at operating temp, taxi out and take off climbing to 9000-10000 feet. It was a steady smooth climb that worked the engine. Then repeat several times. All the bush pilots I know swear by it. I have since grown up and apply that method to every new engine break- in from sleds, outboards and diesels. We break in diesels on the dyno as it’s controlled. Some equipment can be difficult to get a proper break in due to its application.
Once broke in, I hardly ever run WOT, especially on outboards. I do however run a two stroke as hard as I can, always.
I have had many people comment that my equipment seems to put out more hp then theirs, when theirs is the same make and model.
Just my experience. Not everyone will agree, but it works for me.
And proper preventative maintenance is crucial.