The reason we healers DPS

[Shurrikhan]

You're getting into min/max nitpicking that only matters in EX/Savage. In that content, every GCD matters. This goes back to what I just said: non-EX/Savage is not a big deal or it's cutting edge and must be approached the same way EX/Savage content is? It can't be both.

The exclusion of healer DPS, especially in casual content, is more analogous to a melee refusing to use their combos than to subtle aspects of optimization.

Being literally idle or actively wasting MP is no more forgivable for a Healer than for a Tank or DPS. It doesn't matter if it's casual, Savage, or anything in between.
If you wouldn't be okay with DPS neglecting their Abilities (toolkit), taking breaks mid fight (idle time), and/or standing in stuff (wasting healer MP and by extension, further time), why would possibly forgive what amounts to the same in healers alone? That is a massive double-standard.

There is no "ABC" rule. Perhaps that is your personal expectation and opinion but bottom line is what another player is doing (or not doing in this case) is not your call. It's not against any rule. It's not a violation of TOS. It's not harassment. It's unreportable.

Not in the ToA, true. But it is a bare minimum guideline for not being a jerk to your team. Not every rule you ought follow should be due solely to threat of punitive legal measures.