I think we have some agreements in there, and it wouldn't be a problem for me to try and boost the Class as a whole. The weakness of the Warlock class is that it's benefits are frequently dependent on DM fiat. How often will the party be able to get short rests as opposed to long rests, for example, or how many ritual spells will a Warlock find on his adventures in order to put into the Book of Shadows, etc.
For me, the Hexblade essentially addresses some points but not others and is unsatisfactory because of the fluff. If I were to include another Patreon type, it would have been The Undead, like a Lich or a Vampire. That has great roleplaying potential. The Hexblade is contriving a source just to justify a mechanical aspect of the class. It has no flavour.
Looking over the Hexblade features again, I'd say that:
- Hexblade's Curse is basically a souped-up version of the Fiend's Dark One's Blessing. It should, therefore, replace it for the Fiend's Warlocks (or at least combine with it - with the extra stuff being recovered after a short rest).
- Hex Warrior has the aspect of Weapon and Armour (and Shields) proficiency and the Charisma modifier to attack. I think that the proficiencies should just automatically be part of the Pact of the Blade (at level 3), while the Charisma modifier to weapons just be included in the Invocations (maybe just combining with Agonising Blast, perhaps).
- Accursed Specter, Armour of Hexes and Master of Hexes could just be made into level restricted Invocations also.
The difficulty of the Hexblade Expanded spell list is the trickiest thing to manage, although some of them could just be added to main Warlock lists, possibly.
To boost the Warlock Class as a whole, I would:
- Combine some of the features to make them more potent. So, for example, the Pact of the Tome automatically includes Book of Ancient Secrets, Pact of the Chain automatically has Voice of the Chain Master and Pact of the Blade includes proficiency with Medium Armour, Shields and all Melee Weapons. This would free up some much needed slots for other Invocations.
- Expand the options of the Class, with a few more spells, more Invocations and even a few more options for special forms of Familiar.
- Regulate some of the DM fiat aspects into the Class design. So, for example, the number of Rituals a Warlock can have is listed per level (as happens with a Wizards and their spell books) rather than just leave it up to the DM to provide opportunities to locate or steal Ritual spells in play.