What I'm hearing from the OP seems straightforward: He doesn't like the 6th level features of either the hexblade or the shadow sorcerer. Guess what? Neither do I. I don't care for pets, typically, and both of these features give the subclass a pet relatively late in the character's progression. It lacks elegance. One solution would be to simply homebrew new features for both subclasses.
For the hexblade, one approach could be to give the benefits of having a specter--but without actually having a specter. For example: "When you slay a humanoid, you gain temporary hit points equal to 5d8+Cha modifier. While these temporary hit points remain, you gain an extra attack that does weapon damage plus 3d6 necrotic damage. This ability refreshes on a long rest." Seems like an awesome 6th level ability to me!
For the shadow sorcerer, you could do something similar--simply reflavor the hound of ill omen as a shroud of magical darkness that does damage every round to a single target and gives that target disadvantage on saving throws to resist your spells. Alternately, give the shadow sorcerer additional cool shadow-themed spells that aren't counted against their spells known--like shadow of moil, maddening darkness, shadow blade, etc. I like either option--or both!
For the hexblade, one approach could be to give the benefits of having a specter--but without actually having a specter. For example: "When you slay a humanoid, you gain temporary hit points equal to 5d8+Cha modifier. While these temporary hit points remain, you gain an extra attack that does weapon damage plus 3d6 necrotic damage. This ability refreshes on a long rest." Seems like an awesome 6th level ability to me!
For the shadow sorcerer, you could do something similar--simply reflavor the hound of ill omen as a shroud of magical darkness that does damage every round to a single target and gives that target disadvantage on saving throws to resist your spells. Alternately, give the shadow sorcerer additional cool shadow-themed spells that aren't counted against their spells known--like shadow of moil, maddening darkness, shadow blade, etc. I like either option--or both!