Honestly, I think it's one you can cleanse more often than you think.
Doom comes in four variants, so far as I can tell. (Sometimes under different names.)
1. Doom which you can cleanse via Esuna. This can be actual Doom (as in Dun Scaith or the fight with the Queen in Delubrum Reginae, where the tankbuster also inflicts Doom) or the same mechanic under a different name (as with the first boss of the Dead Ends). Healers can cleanse this one, obviously.
2. Doom which you can cleanse via heal-to-full. Arguably the most common, and also one healers can deal with. Seat of Sacrifice, Orbonne Monastery (T.G Cid), final boss of the Dead Ends, etc. (Bonus points to the Dead Ends for being the only mainstream duty I can think of with two different variants of Doom, and the only duty I can think of at all that has two versions of Doom which can be cleansed.)
3. Doom which you can cleanse via environmental mechanics. Sunken Temple of Qarn, mister angry eyeball (Anghra Mainyu in World of Darkness), etc. Can also occur under different names, like Mortal Flame in the Grand Cosmos. Can sort of be cleansed by healers using Rescue, in the mechanic that I refer to as "the piano of gentle correction". (Because when rescuing those who didn't recognize Mortal Flame in the Grand Cosmos as an environmental Doom variant, the piano was a convenient piece of furniture to rescue them across.)
4. Doom which has no cure or counter, and where the healer's only option is to prepare to spend 2400 MP and pray Swiftcast is off cooldown. Sometimes it's just flat out "you have Doom, bye", but it often appears as stacks where you get one when you fail a mechanic. In that case it'll usually be Twice-Come Ruin (two stacks converts to Doom and kills you), or Thrice-Come Ruin (three stacks converts to Doom and kills you). Sometimes content will give you one stack of one of those to start with, or the way in which you resolve the mechanic requires you to take one stack. As with the others, it can appear under other names but functionally identical mechanics. Occasionally it'll be a variant meant to enforce a tank swap, as in the EX version of the Ultima Weapon fight, or the current Unreal.
So, three out of the four variants are ones a healer can cleanse in some way, though I grant the third one is kind of iffy at best since Rescue is janky and terrible.
That said, you're not wrong that we have seen a lot more of the fourth one in Shadowbringers and Endwalker. Twice-Come Ruin (with a timer) in Delubrum Reginae, and Thrice-Come Ruin (with no timer) in Delubrum savage... a number of mechanics in the 8-man savage fights that used Twice-Come or Thrice-Come Ruin, even a few instances in normal content.