TallIan
Explorer
Honestly, the pact boon features should have been baked into the class separate from the invocations. So as a warlock rises in power, the pact boons increase (e.g. blade=extra attack; chain=more powerful minion abilities; tome=more spells and esoteric knowledge). But as it stands, the pact boon invocations are, for the most part, invocation taxes.
I've always thought this was deliberate. Some Invocations are taxes for some builds but it allows a excellent level of customisation (especially if you are not worried about optimizing).
If you want a melee fighter you'll need Thirsting Blade and Lifedrinker; if you want to be a back line "archer" you'll need Agonising Blast, Repelling Blast and Eldrtich Spear; want to be the master of social interaction? Beguiling Influence, Bewitching Whispers and Mask of Many Faces. There are option to be a primary ritual caster, a scout, a bookworm... Far beyond the simple choice of Fiend Blade pact for melee, Fey Tome'lock for charmer, etc.
Not having them built in allows a great level of hybridisation, you can take all the social interaction buffs and blade pact, to be able to sneak a weapon anywhere, either as a back up in case things go south or an assassin style character.
This thread really has made me reconsider the blade pact, at the very least as an interesting build. You are behind a fighter in DPR, you should be, but a fighter doesn't have access to misty step to bypass the evil wizard's minions, or darkness and devil's sight, to dark bomb a big mob of beasties and have disadvantage on all hits against him while getting advantage on all his own hits.
The only thing I really think is lacking is an invocation for medium and maybe heavy armour, although I would be tempted to offer medium armour directly to Blade pact.