I wouldn't say there was no reason to use Cleric Stance and DPS back then. Here's the thing, DPS was absolutely optional during ARR, but it's still optional today in nearly every corner of FFXIV shy of EX and beyond, and even there a lot of fights don't necessarily require healer DPS once a party has started updating their gear. The key differences between then and now are that: enemies had nastier, more frequent auto attacks that could crit; tanks were less durable; our healing tools were far more limited and we could very rarely heal and DPS at the same time; but most importantly of all, our perception of the game as a community was different.
Back then, how powerful and helpful healer DPS was wasn't well known, not to mention Cleric Stance was an extremely punishing ultimatum that many players simply weren't comfortable juggling while other players were relying on them, especially when a tank could die much more quickly than today. At the same time, no, seeing a healer in Cleric Stance was not an indication of a bad healer, but you often would see healers that simply didn't and would either idle or spam Cure/Physick on the tank even if they had full HP in case they might take a nasty auto attack crit. Over time, as our familiarity with the game grew, our understanding of healer DPS developed over time. It was the later half of ARR and going into HW that people started to realize how pointless it was for a healer to do nothing or waste overhealing on a tank that doesn't need it and started to promote DPSing when healing was not required. But even then, that doesn't mean we already had the hyper aggressive DPS spam environment we had today.
That is more a product of how heavily power crept our healing tools are for an environment that asks for a fraction of what we're capable of so infrequently that you're more likely to forget to heal because it's been so long since the party last took damage than you are likely to not have enough healing.
