A solitary Hag with the ability to grant curses is common in various folklore. Saying it should be otherwise, are are suppose to be in Covens is ignoring the materials upon which the monster is built.Hags are suppose to be in Covens, thats their natural habitat and where they have power. Lone Hags should be RP encounters bringing fae terror, or give them some Troll minions if you want the PCs to get some close up melee
Also, the adventure paths are awfully popular, and as far as I've been aware the fights aren't tuned as you describe.
A solitary Hag with the ability to grant curses is common in various folklore. Saying it should be otherwise, are are suppose to be in Covens is ignoring the materials upon which the monster is built.
Why ask if there are stories about solitary hags that curse when you acknowledge they exist in the second half of your sentence? The question is not whether the Coven also exists - it is whether there are folklore origins that are the solitary hag, and we both agree there are.Are they though? The stories of the three sisters/three muses are the material upon which thes particular monster is built, similar stories about solitary crones may have overlaps but do they need to be the same creature?
And the Hags discussed in the monster manual lack key features common to their folklore origins, the Hags in the monster manual differ from the common Hag of folklore. That is the issue we're raising.I’m all for creating unique solitary monsters that have their own abilities - if you want Baba Yaga as a minor fae goddess in Hag form with unique strengths, curses and a flying pestle, go for it - but thats different to discussing the Hag in the Monster Manual.
Best typo ever. And so true.5E monster design sort of falls between two stools.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.