I agree with you that there's regularly a bunch of nonsense posted about Disc, but unfortunately you're adding to that right now.
It's completely not true that Disc requires a good or organized group to perform well. I raid with groups varying greatly in organization and skill. It's not uncommon for some of them to be drunk, clearly not paying attention, distracted by screaming babies, barking dogs, and who knows what else.
Here's the deal about Disc - it's a *flexible* spec. Mythic robots like Sups don't have to care about flexibility because all of the crazy silliness that normal humans experience don't apply to him. So he can do his thing and experience a very similar raiding environment from pull to pull. That's what it means to raid at the very high end of progression - CONTROL. Everyone knows what to do and they do it over and over, iterating slightly and finally kill the boss when their cumulative iterative improvements allow it (combined with good RNG).
Instead of control what normal humans experience is *surprise*. Like, *surprise*, our main tank spilled beer on his keyboard and is cleaning it up during the pull, so how should my healing adjust to account for that? The "best Discs" very rarely have to deal with that. If that actually happens during high-end progression, they just accept a wipe and try again.
A big problem is that Robot Disc, healing in a very regimented, rote, and predetermined manner, actually only applies to a very small subset of raiders, those on the highest end, yet the regard in which they are held and the healing analysis that accords with *their* experience is entirely out of line with their population. The rest of us deal with humanity and everything that means.
So what do normal Discs have to do to excel? We need to evaluate our context. How many players are in the raid? Is there a Holy Pally? How strong are the tanks? Are any of the DPS/Healers bad at avoiding damage? Whatever knowledge we have before the pull even starts helps.
Although Legion Disc is the worst reactive healer spec, we still have some capacity in that regard. PWS, Shadow Mend, Plea, and PWR all have reactive components. Pain Suppression doesn't have to be used on a tank - it's a great, if rarely usable, emergency heal.
Here's a log of a solo-heal 9-player normal Skorpyron, including 34 casts of Shadow Mend.
And this, in what could only be described as a ridiculous clusterfuck, probably the farthest thing possible from "good players playing in an organised and controlled manner", is the top Disc parse currently for normal Aluriel.