Is it fun?

[Rilifane]

Damn that sounds wild!
What MMO(s) had 70-80% healing uptime?

RO, Flyff, WoW and Rift in their earlier stages plus pretty much every somewhat older asia MMO like Perfect World etc.
RO and Flyff had a different combat system and you spent the majority of your time juggling a myriad of mini buffs while healing but letting some of them fall off was just as dangerous as sleeping on healing itself. Depending on your leveling partners and areas you spend more time healing or debuffing enemies but dpsing on healer wasn't a thing unless you were specifically build for it but then you were more of a somewhat self-supporting caster that partnered with actual healers rather than dpsing while filling the healer role.
WoW and Rift both had very tight mana management, fast and strong heals were reserved for emergencies. You spend the majority of your time constantly precasting heals and canceling the cast last second if it would overheal while keeping regens and buffs up. Not just in endgame raids but regular dungeons too. It wasn't because people were bad and uninformed either, it played the same on WoW classic. The way to go was steady, efficient healing so you had the resources for emergencies, strings of crit hits and general bad luck with random mechanics (like a dps getting shot in the face 3 times in a row from something that targets anyone at random).
Even now the Disc priest, which mostly heals through dpsing, spends more GCDs on healing than any decently played healer in FFXIV.

[Almagnus1]

RO, Flyff, WoW and Rift in their earlier stages plus pretty much every somewhat older asia MMO like Perfect World etc.
RO and Flyff had a different combat system and you spent the majority of your time juggling a myriad of mini buffs while healing but letting some of them fall off was just as dangerous as sleeping on healing itself. Depending on your leveling partners and areas you spend more time healing or debuffing enemies but dpsing on healer wasn't a thing unless you were specifically build for it but then you were more of a somewhat self-supporting caster that partnered with actual healers rather than dpsing while filling the healer role.
WoW and Rift both had very tight mana management, fast and strong heals were reserved for emergencies. You spend the majority of your time constantly precasting heals and canceling the cast last second if it would overheal while keeping regens and buffs up. Not just in endgame raids but regular dungeons too. It wasn't because people were bad and uninformed either, it played the same on WoW classic. The way to go was steady, efficient healing so you had the resources for emergencies, strings of crit hits and general bad luck with random mechanics (like a dps getting shot in the face 3 times in a row from something that targets anyone at random).
Even now the Disc priest, which mostly heals through dpsing, spends more GCDs on healing than any decently played healer in FFXIV.

That's one of the things I missed about WoW healing, especially WoW vanilla. You played a healer, but you were rarely DPSing because you were punished WAAAAAY to harshly for it.