Have healers, in the vast majority of PF groups and even statics, been excluded from joining parties?
Now, I haven't read that entire thread, but from what I have gathered from the start, healers find the role unengaging and they don't feel needed in content. The first, unengaging role, that is sorted by rehashing their kit, give them different DPS options, Scholar can be a DoT healer etc. But that is a separate issue to the one where healers don't feel needed. Paradoxically, the role that was not included, does not indicate an issue with that role itself, it is an issue in the rest of the variables.
To put this into context, go back to Ramuh EX, if things were as they were on release, it would have been the norm for tanks to be replaced by DPS, or one DPS and 1 healer for safety. It wasn't the tanks fault that they were going to be excluded. The issue was the mechanics around Titan Egi. Titan Egi was the problem, not tanks, hence why Titan Egi got changed. Now, to be clear, this is all because Titan Egi could completely ignore the tank swap mechanic, you don't have the fail states of a tank failing to swap, or getting enough orbs, which also leads into more orbs being available than would normally be, making those mechanics easier as well. It was just easier to exclude a tank.
Going onto Healerless Ultimates/Savage/Extreme. The issue is not that healers aren't needed, you objectively need healing, it is just that the fight and other role kits are strong enough to invalidate the healer. It isn't the healer's fault they are excluded, it is everything else, whether that is too much healing on tanks or not enough damage going out that they cannot keep up. So, just like with the tank example above, the issue isn't healers, it is what is left. The difference, however, between this case and the one above, you aren't seeing more and more groups getting rid of healers, because it is still easier and safer to bring a healer. Hopefully, you can notice the difference, in one case, it was safer and easier to exclude the role that was being left out, in the other, it is safer and easier to INCLUDE the role that is being left out. The only reason healers are being left out is for the challenge.
Going into more casual content, if the healer feels useless, again, that isn't an issue with the healer, it is an issue with the environment they are in. Whether there is not enough damage going out or it can be too easily healed by other roles. It is the same as above. However, I split this up because the skill level required to negate the healer's efforts is lower. This also means that higher skilled players are going to have a much easier time invalidating the healer, making the issue seem worse than it actually is for that demographic. Go to lower skilled players and the issue isn't as prevalent. You are going to have that DPS get hit by an AoE, that tank might not mitigate as well as they should, the DPS might not be optimising damage as well making things take longer to kill (and thereby eating into resources). Again, for your average group, it is safer to go with a healer to account for those mistakes, than a group of skilled players who do not run into those issues.
Hopefully this sheds a light onto the differences between what happened to the tanks in Ramuh EX and the healer role as it is now. The same reasoning can then be used for the topic of this thread, the tankless clear of FRU. Is this an issue with the tank role? No, it is an issue with the environment. Is this going to be come the norm? No, it is still safer to bring tanks to the encounter. If there was an encounter that was explicitly harder with a healer, then you could compare that to the Ramuh EX scenario, however, that has never been the case.
This shouldn't come as a shock either, tank, healers and encounter design are all interlinked and there is an every changing balance somewhere that moves based on content and player skill level.