I strongly disagree with the notion that a warlock is a "full caster". The cleric, druid, bard, wizard and sorcerers are full casters.The thing to realize about hexblade is that warlock is a full caster class and is balanced that way.
The warlock is... someone who couldn't cut it and made a pact with some mysterious power and got the semblance of being a full caster. You know one spell per level level 6-9, and you can cast it once. The magical resources the full casters can bring to bear are far greater. It's a fun class, and a useful one, but it's not really a full caster.
It shouldn't be as good as a tank as a paladin, barbarian, etc that are melee classes. It should be in the same category as college of valor or swords bard, or bladesinger wizard. That's its target level of melee competence.
As I said above, a hexblade uses almost all their resources to be a 2nd rate melee fighter. The bard or wizard have much more magical resources at their disposal.