The prop "absorbs the engine's power". That's the way propeller text books say it. They say, "absorbs".

The diameter and pitch together load the engine, give the engine something to work with. You need a combination of diameter and pitch that suits the power of the engine. Once you're in the ballpark you can focus on the two details.

You choose pitch to control the speed and climb of your airplane. After you've found a prop that combines dia/pitch to suit the engine, if the airplane is too fast for your purpose, the prop pitch needs to be adjusted. We can't adjust almost any of our model props, so we just buy a differently branded prop to get the different pitch. If the prop with the different pitch now lets the engine run out of it's power range, we can adjust with more or less diameter. Since we can't adjust......... etc.

Keep in mind that pitch isn't a perfect nor an accurate specification. It's really just a suggestion of how that model prop should act. Pitch is a very complex detail. Ain't no sound bytes that really work worth spit about it.

And keep in mind that we're slapping these props onto a broad range of engines and an even broader range of airplanes. The airplanes are extremely variable in how they affect any prop's performance. So we often need to try different combinations of dia/pitch that are not the "best" suggested one for the engine. We've got to match the prop to both the engine and the airplane. And that often results in using a prop that wasn't the "sound byte best" for that engine.