1: I've done ultimates as a healer. The reason that Dungeons are used as the 'strongest showcase' of why Healers need to be addressed is because almost everybody does dungeons. Only 10% of players participate in Savage, or only 4% participate in Ultimates, or whatever varying percentage it is per world. But almost every player is going to do the easier content like a dungeon, a roulette, a normal trial, because they're doing the story, or they're levelling the job, or they're doing it for tomes. The idea that a job, or in this case, a role, should be 100% reliant on the difficulty of the content to determine whether it's 'engaging' or not is asinine. I shouldn't have to do week 1 Savage and Ultimate to have fun with my Job, I want to be able to go into EX roulettes and have fun on it there too.
2: Trying to get the 'before you mention the thing that completely obliterates my stance' doesn't prevent it from obliterating your stance. Nobody is saying that the healerless TOP clear didn't take skill, or luck. The fact that it happened at all is the issue. It should not have been possible in the first place. The fight has a mechanic that demands 'You Healer LB3 this or you die'. Trying to bend over backwards to defend the fact that Healers are not needed in the hardest content in the game with 'oh well it took a lot of skill, and nobody else does it because it's so much more stress/skill required and people prefer the path of least resistance' is comical. Because Yoshida himself said 'if you want a challenge, try Ultimate'. Well, that ultimate (DSR at the time) was solo-healed. TOP was no-healed. For a game that is built on the Holy Trinity, being able to remove one of the three Trinity members entirely, in the hardest content in the game, is a stain on the game's design. Please do remember that, when it was discovered in ARR that Ramuh EX could be cleared without a Tank by having Titan Egi tank it, it was hotfixed almost instantly. Tanks are unrequired? Emergency patch! Healers are unrequired? /shrug, apparently.
3: Is this your first expansion, by any chance, because people have said that for every expansion since SHB, including SHB. We have not seen an increase in healing required that is anywhere close to the increase in healing output we receive in each expansion. Our HPS increases vastly out-pace the required HPS in content, every time. The line 'we will have to heal more, thats why they're giving us more healing tools' is the stalest copium on the market
Stormblood dungeons as SCH were the perfect middle point between 'accessibility' and 'engaging/challenging'. If you wanted to just chill your way through the dungeon, you could just Broil things, or Miasma 2 occasionally, or even just AFK (not recommended, but it won't cause you to 'fail' the dungeon). If you wanted to be more 'tryhard', you could Bio/Miasma, Bane the packs, use Miasma2 for movement and Energy Drain to make the movement a damage gain instead of a loss, making sure to Shadowflare at a time where you don't need to overwrite it with Soil in the near future, etc. The 'pain point' of Cleric Stance was removed with SB. We didn't need the 'accessibility' of having every DOT condensed into one, once-per-30s button press.
edit:
You're asking us which specific piece of content. We're saying 'it doesn't matter which piece of content, because it's not the Content that was the entire source of the Complexity back then, it was a combination of the Job design AND the Content design'. If the Content design sucked, then we could make up for the lack of challenge from the Content by interacting with more of the challenge available within our Job's design. Now, we're entirely beholden to the Content design, hoping that we get to have fun. And if the Content design falls flat (see P6S, P7S, P11S to an extent), then the Job design we no longer have, cannot make up for the lack of engagement from the Content.