80% eh? That smacks of a made-up statistic to me.

Many add-ons, including (almost) all of the ones Dawn discussed, are about presenting the information the game always gives you in a more accessible way. In fact, that was her thesis statement: "How information is arranged is what really sets each raid frame apart, and the default UI doesn't allow you to customize that information enough". The game presents information in a generic way that is reasonably appropriate for all classes during solo and small-group play, but it is up to the individual to customize the flow of information to their role, playstyle and learning preferences.

Now, Dawn does suggest that it will "take some practice to get used to reading all this information in combat" in reference to her grid setup; however, this is information that the game does give you already. The default UI makes you click through your party members to see a lot of this information, however, while third-party raid frames will show you the information in parallel. Given that it is all information the healer requires, I don't think you can reasonably argue that clicking through your raid frames between each heal to make decisions is "less distracting".

The only addon I see in this discussion that provides information not available in the default UI, is Ingela's Rapture; tracking the internal CD on Rapture will make most Disc Priests more effective. So are there four addons here we need to turn off to justify keeping it?

As for eschewing raid frames that show incoming heals in favour of discussion over voice chat, that's just crazy talk (literally!) If healing is so trivial that you have time to micromanage casts over Vent then you probably don't need to coordinate at all. Once you know how to read your raid frames properly, you can triage heal targets at a glance; I can't see what would be gained by requesting that information verbally.

The point here is to take all of the information that you need and arrange it for faster and easier assimilation. Suggesting that replace the information with guesswork and committe-based healing is counterproductive.