Yes, you're right, there are mistakes in 'normal' parties, and you have to cast healing actions on people because they unexpectedly stand in danger sometimes. But you're also wrong, because the picture shows the opener, and my example is just one of... pretty much any fight in the game, where there is no damage for the first 20-25 seconds of the fight beyond a customary raidwide. M4S is the same, P12S is the same, etc etc, the 'haha here's a raidwide to burn your prepull shields' has been a thing for years in raids, to the point where it's kind of a surprise if the boss does something else first (e.g. opening with a tankbuster). The 'healing actions' you're on about, even in a breakdown of a 'typical fight' as you put it, wouldn't feature on those pictures either way, because the healing simply isn't needed at the point in the fight that the pictures depict (unless someone somehow stands in the death wall at 15s in). With incredibly few exceptions (so few none come to mind), the given boss literally does not do anything that would warrant you needing to heal, there is nothing for players to 'oops I stood in the orange' with, or 'miss mitigation on', in the timeframe the pictures show. The opener is just the opener, and what happens in each fight beyond what is depicted in those pictures can vary. Sometimes spot healing is needed cos someone stood in bad, sometimes you deviate from the rotation slightly to have your DOT refreshes line up with movement a little better, etc. But you're trying to imply that something was 'hidden' from the viewer, with nefarious intent, when that's not at all what is going on
The only way to have 'healing actions' shown on these opener diagrams, is by being in Savage and having a party that refuses to use any other mitigations (so you have to Fey Illumination/Soil/Seraph as well as the Deploy), which is already bad vibes, or that you're simply pressing healing actions when it just isn't needed (e.g. trying for 100% Medica3 uptime).
edit: I now remember that there are fights that open with 'your HP is now 1, heal to remove this Doom', such as Seat of Sacrifice. They should do that more often. Setting your HP to 1, I mean. SB had like 3 different raids that did it (White Hole, Heartless Archangel, Charybdis in O11S). Especially now that SCH can cosplay a WHM with Seraphism (so they can spit out 520p of healing every GCD via ET spam) and SGE has Pneuma/Philosophia (Prognosis spam with Philosophia being 510 if my maths is right)
On the plus side, tanks like those you describe give us the 'healers should heal' gameplay that some are looking for, due to the aforementioned... let's call them 'playstyle choices'