Ultimately, the whole origin story of the debate was about whether or not it was expected that healers would engage with their DPS actions outside of solo content when the game was in development and during the launch of ARR, which the content of ARR makes clear was expected. "Expected" in this context referring to whether or not the community would engage with it and NOT in the context of whether or not the content demanded it. ARR didn't really have enrages in the same way that we have enrages now, and healer DPS was not required. I believe this indicates healer DPS was perceived by the designers as a reward for good healing. HW was not really a part of that train of thought.
Back during that time, I wasn't really invested in Savage, moreso because I didn't really have a group of people to do it with and I wasn't super invested in trying to find a group, so my knowledge on the finer details of Savage gameplay was more limited. That said, I do know that the combat team royally fudged the testing of savage fights during HW, and it was a big deal that led to an apology and a promise to do better moving forward. I wouldn't put it past them that healer DPS wasn't intended to be required but might have been on week 1 unintentionally, but I can't say from experience. SCH parsed higher than NIN at the time, from posts I've seen in the past, so required or not, I can't imagine healer DPS not being of significant value to raid groups especially since SCH was largely viewed as a required job regardless of whether or not it was required to get clears. Even if the design team attempted to balance fights around healers not contributing damage, I imagine the raiding community would aggressively pressure healers to do so anyway. You no doubt would be skipping mechanics with it anyway, but that of course is the community view and not the design view.
Perhaps that's even why Savage content began expecting healer DPS, because the amount of mechanics that you could skip by having healers attacking was significant enough that the combat design team may as well have been forced into taking it into account, and likely contributed to the decision to axe old Cleric Stance.
I recall forum conversations from HW, and it would very commonly refer to statements that effectively can be summarized as either "As a healer, you should be DPSing. If you aren't DPSing, you're griefing your team." or the other side of the fence that would go "Healers aren't supposed to DPS and I'm not going to." One of the two would go first, followed by the other. Then after both those statements came through, it would be followed up with more genuinely concerned players who'd say things like, "I try to DPS when I can, but sometimes I'm afraid of going into Cleric Stance, or if it's a new fight, I prefer to get comfortable with the mechanics before I try to DPS. It's not griefing." Then you'd have the first camp reassure those players saying "It's okay if you're learning a new fight, or you're trying to get better at healing. What matters is that you're trying your best to help your parties, but it helps to practice getting a few hits in now and then to get comfortable with it." Then the arguments would die down, and then start back up again.