I actually think the rules might have you covered better than ever before.
You can be a celestial warlock, casting True Strike with a bow. You won't get extra attack, but you'll be using your casting stat and (at level 6) adding your charisma twice to the radiant damage of every hit.
This is an interesting build path to explore because it makes you ask, "Do I even need Blade Pact?" Blade Pact gets you weapon proficiency, weapon attacks with Cha, alternative damage types, and access to further invocations. But how many of those apply to a Celestial Warlock using True Strike with a bow?
Weapon proficiency is tricky. Blade Pact says it can conjure a melee weapon or bond a magic weapon. The "melee" qualifier is not repeated for the second clause, so it's unclear if it's assumed to still apply or if you can bond an enchanted longbow. However, Warlocks do get shortbow and light crossbow proficiency, so if we say you stick with those it isn't required.
As for the rest, well, most of them are redundant. True Strike gets you attacks with Cha and Radiant weapon damage, and if you're going this route you're not planning to take the other invocations for extra attacks. So that frees up a lot of invocations for other things, like maybe the Chain Pact route for a more combat oriented familiar.
Let's sketch out some numbers. At 8th level, a traditional Eldritch Blast build or Bladelock using a versatile weapon are making two attacks for a total of 2d10+10 damage, or about 21 damage if both hit. A Celestial Warlock using True Strike with a light crossbow is doing 1d8+1d6+15, or about 23 damage. Really close, though the damage curve is a bit different between one attack and two.
The big advantage of True Strike over Blade Pact is it's costing fewer invocations, and that's not nothing since both the Imp and Sphinx of Wonder are doing an average of 12 damage on a hit. The big advantage of the Blade Pact route for multiple attacks is that it scales better with things like Hex that add damage per hit.
But how's it look at 12th level when EB and Blade Pact are making three attacks? That's 3d10+15 vs 1d8+2d6+15, or on average 31.5 vs 26.5 damage. True Strike with a weapon is falling pretty solidly behind, and the numbers are even worse if you throw in Hex. The advantage over EB is that you're using a weapon, and magic weapons are often stronger than a Rod of the Pact Keeper. The advantage over Blade Pact is that you're devoting far fewer invocations, and it really depends what use you put those to.
So I think we get back to my previous assessment. A Celestial Warlock using True Strike is about on par from 6th-11th level and falls behind a bit once it's competing with three attacks. But if you're investing those freed up invocations wisely, or don't expect the campaign to spend much time in those higher level brackets, it's not a bad character idea.
