A lot of the invocations are non-combat oriented: Ghostly Gaze and Ascendant Step seem pretty cool (though I've never seen it used in play), Eldritch Sight and Mask of Many Faces are quite nice (I have used those)... there are things like Whispers of the Grave, Visions of Distant Realms, etc. as well. And of course Tomelocks can get rituals like a wizard, except actually a bit better than a wizard since they get them from any class.
Or worse since you must find the rituals you want to add in the game instead of being allowed to potentially choose 1-2 per level. But overall I agree - tomelock provides the best out of combat utility.
I think there can be quite a bit of utility there; maybe not to the extent of a wizard, but more than a sorcerer, and different than a bard.
I don't even think I'd put it at more than a sorcerer. You get the ability to disguise self at well vs the ability to disguise self a few times per day that a traditional caster gets. I'm not positive that making that be at will really has a huge effect on anything but character conception.
The tomelock with a book of shadows (1st invocation take) and cantrips from any class covers the ritual casting and some of the more useful cantrip uses.
Then you take Agonizing blast since your set up to only cast a big spell on turn 1, you will want your at will option to be better.
That leaves open 2 invocation slots. Let's look at what we can do with those
EYES OF THE RUNE KEEPER You can read all writing.
Not great - but I suppose it helps in adding ritual to your book of shadows
GAZE OF Two MINDS You can use your action to touch a willing humanoid and perceive through its senses until the end of your next turn. As long as the creature is on the same plane of existence as you, you can use your action on subsequent turns to maintain this connection. extending the duration until the end of your next turn. While perceiving through the other creature's senses, you benefit from any special senses possessed by that creature, and you are blinded and deafened to your own surroundings
In a party with a really good scout that scouts ahead this could be pretty good.
MASK OF MANY FACES You can cast disguise self at will. without expending a spell slot.
Very fun but not particularly useful - though maybe with this and the actor feat you could make something nice. That combo is my favorite thus far.
MISTY VISIONS You can cast silent image at will, without expending a spell slot or material components.
I've actually used a warlock with this invocation for a session. It was quite fun but I'm not sure it was particularly useful.
ONE WITH SHADOWS Prerequisite: 5th level
When you are in an area of dim light or darkness, you can use your action to become invisible until you move or take an action or a reaction.
Terrible ability as you can't even attempt to hide after becoming invisible.
BEAST SPEECH You can cast speak with animals at will, without expending a spell slot.
Not impressed
BEGUILING INFLUENCE You gain proficiency in the Deception and Persuasion skills.
At least it's useful.
DEVIL'S SIGHT You can see normally in darkness, both magical and nonmagical, to a distance of 120 feet.
Great for non-darkvision races
ELDRITCH SIGHT You can cast detect magic at will, without expending a spell slot
When a ritual has essentially the same effect you might as well not bother.