FWIWYea, I hadn't considered it at first, but it would go a long way to eliminating the palilocks and the coffeelocks.
It's a fair question. I think the way it is presented is that Warlocks should play similarly with similar roles to Sorcerers or Wizards, when in reality I see them being more equivalent to Rogues or Monks.
I don't know that I would go half-caster. I like thinking of Warlocks with tons of at-will spell abilities, which is where cantrips and most invocations come in.
I agree that the spell granting invocations can be a problem. But I think the best way to solve that would be to wrap those into your patron. Currently, patrons provide options for bonus spells that warlocks could select (but don't have to) with their Pact Magic. Instead, provide level appropriate spell invocations themed around their Patron bonus spells. This limits the number that they can get, but also doesn't force the choice while allowing Patrons to have themed invocations. Then the only other way to gain spell per rest invocations would be Mystic Arcanum / Greater Invocations.
Of course, this would then also necessitate a change to the Warlock capstone.
I agree in play i describe warlocks as spell fighters - the spam spell attacks like fighters spam wpn attacks - with the hexblade being realky the more direct "my spell looks like a weapon" variety.
I personally dont think invocations for low-end limited at will spells or bigger level appropriate once per SR spells are a problem
But...
Absolutely have more patron specific and boon specific invocations and have all the spell ones divided among those.
As an eyeball estimate i would start with every oddlevel being an invocation odds like sneak attack dice.
Every even level being a pact or patron feature alternating.
I would consider a design where each patron had features fueled by "boon points" and boon points were gained based on your pact choice by LONG REST plus pact specific means.
This create a semi-mechanical manifestation of "services" in that doing these pact specific things can replenish some points during short rests.
Perhaos tome might be submitting scrolls to the master by means of ritual destruction.
Perhaps chain might be something to do with sacrificing beasts fey etc by ritual.
Perhaps Fiend involves sacrificing something holy or unholy?
Just off the cuff ideas. But they should be there for occasional quick surges not assumed everyday.
However, in truth, that may make a class festure too campsign dependent. So a nice idea with potential flaws.