regardless of your internet speed or if the fault is on the user side and your page load is over 3 seconds, you will leave the site
As both a developer and an end user, this drives me batshit.
Seemingly no one has figured out that if users are bouncing due to page load times, maybe the problem is actually because your page that was supposed to be, say, a recipe for a bologna sandwich doesn’t need to first load an embedded autoplaying video, an external jQuery library, a cookie notice, three time delayed popovers, an embedded tweet, and a sidebar that dynamically loads 20 irrelevant articles, and a 2600x4800 100vw headline image that will scroll up at half speed before the user can even get any of the content into the viewport. Just a thought. I don’t care what your dog-eared copy of Engagement For Dummies says. It is actually wrong.
I have made the business I work for quite successful online by taking all of the alleged “best practices” things that clearly annoy the shit out of everyone, and then just not doing those things.