Sure. The content blocking API is more secure as it doesn't allow any code by the extension to run and modify a web page. And so logically sounds like it should

Sure. The content blocking API is more secure as it doesn't allow any code by the extension to run and modify a web page. And so logically sounds like it should use less cpu / power. It is also true that it is a much, much inferior ad-blocking solution. If a feature is popular, it doesn't make sense to remove it. Instead, you can choose to make it opt-in. That both Apple and Chrome haven't opted for that speaks for itself - it is clear that they are prioritising crippling adblockers than letting users control what code run on their browser.