Possible cause of slow, erratic web site display

Do excessive or badly behaved ads cause slow and erratic display of web pages? I have noticed that in some web sites, most notably ArcaMax.com, a high population of ad frames at random locations placed to obscure the text of an article, seems to cause blocks of article text to flash on briefly scrolling up or down into them, then wait several seconds or up to a minute or to before fully appearing. Even text that is ALREADY being displayed DISAPPEARS completely when scrolling up or down INTO an ad frame, as if the browser (Safari on iPhone with iOS 12, 13, or 14) can't display text it ALREADY possesses while loading (or reloading) an ad frame, and thus blanks out the text until the ad is completely loaded before reloading that block of text from scratch. This is very annoying in trying to follow the logic of an article.

Along with this, the scrolled position of the text jumps unpredictably when ads that "lost the race" to get there first finally arrive in the upper portion of the page after scrolling past their locations. This behavior is very annoying, and when accessing a page on a metered access path, I suspect that the unneeded reloads are padding the data usage count, cheating the user out of paid-for data.

Has anyone else noticed such effects on iPhones or any other device? I have seen it on the iPhone 7 when opening an email from the list (or from the up-and-down arrows), and on several web sites, but most often on ArcaMax.com, which has articles linked from the Proud Progressive newsletter email.

And does anyone know how to tweak ad-blockers to reduce the ad population and/or ensure a stable, non-jittery display despite this?