Right, I don't mean that they literally don't heal at all, but that they may play the how-low-can-you-make-the-tank's-hp-go-without-killing-the-tank game and then for whatever reason (inexperience or distraction) they lose at it. And this would apply to any non-healing spell they'd be using instead of a healing spell.
That's a fair opinion, but do you think that the game's direction agrees with you? And to be fair, fun is subjective, while there is some objective measure toward making things easier to reduce potential conflict between different types of player. That said, I'm not saying that simplifying tank/healer has to be because of this one specific reason. There could be others or even a combination of factors. Nevertheless, there seems to be an overarching theme from making it easier to complete solo quest to simplifying crafting/gathering, etc.
So when you say that it's worked in the past, the devs might not agree because they probably saw a problem to fix.
In addition to my response to GrimGale, I didn't intend to imply that they're necessarily malicious in not healing, but the result is still a lack of healing.
As for rarity, I think sometimes people can make a small problem bigger than it is. Regardless of my stance on how certain things should or could be done, I rarely ever see problems in the nearly four years I've been playing this game running dungeons, trials, and raids. And of those problems, most are simply annoying but you can get through it and still finish the content just fine and leave.
But one thing is for certain, and that is when playing with random people, you don't always get near ideal situations. And considering the roulette is a major content in this game where you can potentially meet different players of various experience, mindset, skill, or even preparation, the statement "healing is hardly needed" depends on many factors.