Major Homestuck spoilers ahead; hover over them to view them.
I saw a comment the other day on /r/Homestuck to the effect of “Remember when we thought Breath was about freedom? Yeah, right.” I don’t know if the comment was meant seriously or not, but it gave me a moment’s doubt, which in turn led to noticing what I think is an important factor in the Heir and Witch classes.
An Heir or Witch has too much of their aspect. To succeed, they have to work around this.
John Egbert, the Heir of Breath, Act 6 Act 6 Int. 1 thru 4 gains complete freedom when he puts his hand in the Treasure. Being a successful Heir, he recognizes that this is too much freedom to be wielded by one person, and accepts Terezi’s leadership. (This was the original counterexample in the comment I saw, but viewed in reverse.)
Equius Zahhak, the Heir of Void, inherited a place high in the hemospectrum, and used it as a buffer between himself and everyone else he interacted with. Act 5 Act 2, p. 005348 He is eventually killed by Gamzee, who is above him on the spectrum, because he wasn’t able to put it aside and fight back.
Jade Harley, the Witch of Space, grew up on an island in the Pacific, isolated from the rest of society except for her grandfather and Becquerel. She was fully aware that she was not exactly the most socially apt person ever as a result, and she submitted to others’ guidance often on that topic – for example, she was by far the most receptive of the beta kids to Karkat’s shipping grid.
Feferi Peixes, the Witch of Life, was obsessed with caring for people, and practiced this by “culling” her cuttlefish (using a very different version of the term than was used by Her Imperious Condescension). However, she became too obsessed with her cuttlefish and never managed to look past them at the injustices committed against fellow trolls in Alternian society.
Damara Megido, the Witch of Time, Act 6 Int. 3, Openbound III, p. 007298 ends up jumping around the timeline chaotically, destabilizing the Beforan session; after her death, she apparently becomes bored in the dream bubbles, and turns to rampant promiscuity to pass the time, although it’s debatable whether that could be considered a failing. Her post-scratch identity, the Handmaid, works in much the same way on Alternia to move it towards Lord English’s desired path.
Mituna Captor, the Heir of Doom, could be construed as either succeeding or failing. Openbound II He reportedly spent his entire psychic power, and a significant amount of his sanity, on “some great act of heroism”. So, uh… I dunno. As the Helmsman, at least, it is more clear-cut: he failed to contain his power and was enslaved for it.