Now lets talk about the real issue of how badly this subclass is designed. It goes to the overall quality of the game if they can't get something simple like this right.
To ask if something is badly designed, you have to know what the intent of the design is, and the context it's embedded in (my favorite example of this is the Juicy Salif, which is a perfectly designed non-functioning juicer).
We can perhaps presume the intent of the hexblade is to have a functional melee-caster hybrid that satisfies the needs of people who want to play a darkly magical warrior of some sort.
The context of this is
- Other melee-caster hybrids (such as the bard and the eldritch knight and a fighter/wizard multiclass)
- The monsters and hazards a PC will be facing.
We don't REALLY know #1, and we only know #2 up to a few examples from the first few levels.
So it's not really possible to evaluate the hexblade objectively at the moment, if our presumed intent is correct.
But note that whether the hexblade is as good as the tome/chain warlock is not really at stake in this assessment, since these are different intents. Whether the hexblade is as big a DPR queen as the eldirtch blast warlock is not a major consideration unless the intent is for them to be equal damage-dealers, which may not be the case.
In design, the goals and the context are pretty vital to understanding if the design was successful, and while we can guess at the goals, we really don't have the context for evaluating them quite yet.