Again, leaving you with very few out of combat magical utility.
Well, sure. You are putting out basically in-combat fighter levels of damage if you do it right.
Shouldn't you end up with as much out of combat utility as a Fighter does?
IWhile there is no guarantee that a single casting of Hex will suffice, given Dispel Magic like effects, a Hexblade can easily mix up their tactics to prioritize damage avoidance.
Also, if you have a safe spot to rest for an hour, you probably have a safe spot to rest for 2 hours. (sometimes this won't work, but it isn't plausible that it happens very often).
So usually if Hex is down, short rest, cast Hex, and short rest again. At level 5+, Hex lasts
8 hours while short rests are 1 hour long.
Warlocks get short rest slots and buffs that last 8+ hours from them.
I've had Adventuring Days where I have not taken any damage, through a combination of luck, tactics, and not to be repetitive, luck again.
I've also had Adventuring Days where a poor roll has resulted in a single point of damage from a half buried caltrop takes down a Pass w/o Trace spell.
Yes, concentration is a bitch.
Warlocks limited slots is one of the reasons why concentration based spells are
less useful to warlocks. With a normal caster, losing concentration costs you an action and a daily slot. Your concentration spells are already super efficient, however, so if you are using concentration based spellcasting you probably have the slots to spare over the day.
A warlock has such a shortage of spell slots that losing concentration and replacing it with another spell slot is crippling in that encounter (and until the next short rest).
By using a long-duration concentration spell like Hex and refreshing the slot
after you cast it, you reduce the cost of losing concentration significantly. If Hex goes down, you'll still have 2 slots; you can burn them for in-combat concentration effects (if you want).
A cast of darkness may be higher impact, but it costs an in-combat spell slot. That is very expensive for a warlock.