Comparing it to overpowered top tier feats is not enough to rate something poor. The equivalent of 1+PB 1st level spell slots per long rest makes GCD a strong average.
I compared it to three feats, Fey touched is top tier, but I don't think most would say magic initiate or fighting initiate are overpowered top tier feats.
The resistance is the better part of this feat and the multiple uses are nice, but they are only equivalent to spell slots if you actually use them. I love absorb elements, which is slightly better than this, but I don't think I have ever cast it 3 times in a day, in part because it uses a reaction which is not always available.
Hunter's Mark and Hex are concentration, and rarely last to the end of one fight if you play RAW. But still, as a half feat Fey Touched is GWM overpowered. That doesn't make anything else poor.
I think playing RAW you will generally get more damage per casting of HM or Hex. Even if it does not last an entire combat it does more per hit, so you are going to be ahead on the very first turn you cast it, when the damage matters the most and you will keep pulling further ahead every turn you get to use it. While you may lose concentration in the first battle you use hex, you will rarely get more than 3 or 4 turns with COI. This is especially true since hex works on all attacks, where disarming you or making you do a ranged or spell attack loses the COI damage for that attack.
Also FWIW GWM is not as OP as everyone makes it out to be.
The majority of classes already have cure wounds on their spell list. If you don't already have it someone else in the party almost certainly does. GMD is also equivalent it 1+PB 1st level spell slots, making it almost exactly equal to GCD.
Right, but it sucks up a spell known for most classes to and most classes are not going to take it when other better spells are available. Wizards are who can benefit from it the most, because they have nothing on their list to bring up a downed ally or do any healing at all. Other classes who have healing available are probably going to take or prepare something else.
I think it is rare that someone has cure wounds specifically prepared. Virtually no one has it as a known spell and Druids and Clerics rarely prepare it when better healing spells are available, even at 1st level where healing word and goodberry are the go-tos.
I am playing 6 games right now, of those:
5 player game - Paladin, Warlock, Rogue, Barbarian, Rogue/Cleric (me). No one has cure wounds
4 player game - Ranger/Cleric, Monk, Sorcerer/Warlock, Barbarian, Rogue/Wizard (me). I don't think anyone has cure wounds prepared, although the Ranger/cleric has a lot of healing and it could include this (I just don't remember her ever casting it).
3 player game - Sorcerer, Barbarian, Rogue (me). No one has any healing spells at all.
5 player game - Wizard, Artificer, Monk, Warlock, Rogue/Fighter (me). No one has any healing spells
5 player game - Wizard, Rogue, Rogue/Bard, Sorcerer, Rogue/Ranger (me). No one has cure wounds, the sorcerer is a divine soul and has other healing.
3 player game - Fighter, Cleric, Rogue (me). No one has cure wounds.