I can agree with this. I tend to get quite depressed by the community though.
I think this is the critical point in everything you said though. You're viewing the game the same as so many other people (not that that is inherently bad):
End game/savage is the only relevant content. Everything else is faceroll.
This is simply not true. The sync system, echo (and our ability to remove echo), minIL, and undersizing (including undersized minIL, sync, and unsync) are all there for a reason. Old content is just as relevant as new content. And normal battles can be plenty difficult if you go in with the right set of limitations. People just refuse to play it because they're too concerned with the newest and shiniest material rewards to bother with it. But old content is no less fun than any of the new content. Nor is it any less challenging. In fact, in many cases it's harder. And if you do it with customized parties to up the challenge, the mechanics change. Attacks that used to be no problem become exceptionally dangerous. The healer may be so busy trying to solo heal the tank that they can't cope with any incoming damage unless they use cooldowns. And if a big boss AoE is coming up in 30 seconds, a DPS eats avoidable damage for 75% of their health, but you can't stop healing the tank without falling behind, you'll have to use cooldowns to prevent that DPS from dying 30 seconds later.
You keep saying that there are no situations in which this safety-first mindset is relevant because bosses (especially these days) are designed to be fairly straightforward. Like you said, either the damage is negligible, or it is an instant death. But if you start delving into undersized content and related challenge runs, you'll very quickly find that cooldowns become necessary to use frequently. Then of course there are situations like the one you mentioned where experienced players are carrying.
However, you should also remember that it's not just about preventing deaths. It's also about recovering from it. If a player dies, the healer will often need to use cooldowns to recover from the situation. This is especially true if multiple players die in rapid succession.
It also sounds like you don't solo heal a lot to be honest. Especially not with a party that takes extra damage. There are tons of situations in which healers need to at least double-cast an AoE heal via Swiftcast, etc.