Healers having less throughput for dps was less of an issue when the game launched and solo duties were more limited in scope, usually not having dps checks. Most of the battle content while leveling took place in the world with those little purple quest circles that spawn enemies and via FATEs, so you'd just as likely be able to do the whole healing thing for actual players.

Solo duties could still occasionally be tough; I remember getting my butt kicked in 2013 by the level 30 GLA duty with the bridge and level 20 CNJ duty where you have to help some Adders fight a buncha goats. Keeping them alive eventually led to a steamroll, which is good if they wanted to emphasize healing, but I had to deal a lot of damage, too. Then again, my gear was probably awful cuz I kept picking gil rewards from quests instead of upgrades.

Even when that quest Rollind's talking about was current though, I wiped on WHM once because I didn't save anything for the three swords. I was returning to the game so I wasn't in full i400, but I'm a veteran player at this point. That part of that duty has just always had a pretty tight timer for healer jobs. AST had stronger card buffs and more DoT damage back then, too, though maybe it balances out if you save Astrodyne and Divination for it.