This is not the way to look at the roles of the game. Each of them bring something fundamentally important to the table in order to get clears. You will notice this quickly if the tank goes down and your second on the aggro list, or you if you do not meet a DPS check. These two things are some ways I can think of that will rip the god complex out of any healer. The ability to sustain a group is only one part of the PvE dance.
What I will agree with that everyone will blast me for is that healers should only be given a simple DPS rotation that is extremely difficult to screw up. It is what it is. I've remained steadfast about these thoughts for years now. I've stood by the dev's decision with this approach, and it isn't changing anytime soon. My experience with the difficulty in playing this role in FFXIV differs from what is expressed here. What I can admit to is my scope on healing is limited because I do not do relevant Savage or Ultimate, so I cannot speak about healing requirements for that level of difficulty. However, what I do know is that it would be difficult to call content "Extreme", "Savage", or "Ultimate" if a healer's kit is not needed to sustain DPS uptime.
And that's kind of it, isn't? You'll notice I said "sustain DPS uptime" and not increase it. Healer is a very unselfish role to play. Their healing kits provide sustainability to the entire group, which benefits everyone's DPS uptime by not letting anyone's hit or stay at zero, which ultimately benefits you. While I do think there are some wolves in sheep's clothing out there, who are just DPS players wanting quick queues; I do believe that most healers out there smashing that one button feel that their purpose in the group is next to nothing because their kits have become redundant. It is leaving players feeling this way, where I fault the devs a great deal.
Healers have to constantly deal with the rise and setting of the sun when it comes to their kits. The sun is at its highest when new content is released. Their purpose renewed. Then that sun gradually loses its brightness to the horizon. If there is anything the devs need to fix, it is this. More DPS buttons will not do this, and the healer mains out there know this in their gut.