I do not like Eldritch Blast, and I do not like the Blade Pact Warlock’s design. Some of this I can and will fix; some I won’t.
First: Hairshirts and bellyaching. Eldritch Blast is a cantrip which scales by adding bolts (unique) and deals force damage (unique) and does d10s (not bad!). There’s some balance there, naturally, but… wow. In my ideal world, warlocks would deal poison or necrotic or elemental damage with their starter pistol: damage types which are resistable, work well enough for me to fit as a weapon of their patron, and don’t make them King Ghostbuster.
Second: The Blade Pact. As written, it’s kind of weird; it takes a magic weapon and pulls it into the character, but it doesn’t scale (like EB does), it forces multiple ability dependencies without giving anything useful in return, etc.
At first, I was playing around with defensive hacks; why not make it give you monk-like AC? But that feels wrong for something called “Blade”. Also, there’s the scaling problem, where the blade just won’t scale as fast
Pact of the Blade rewrite
You don’t bond with J. Q. Arbitraryweapon; instead, you have a lightsaber, a close-quarters manifestation of your pact. The concrete benefit of using this weapon — which glows as a candle — is that you may use the Attack action with it (and OA and otherwise use it as a melee weapon in all ways). When you do so, treat the weapon as dealing damage equal to a single blast of your EB, of the same damage type as the EB, with a range of 5′. It can cosmetically look like whatever you want. If you have multiple blasts of your EB, when you take the Attack action, you may take those iterative attacks. Blast invocations apply to uses of the blade, too. Attacks with it are spell attacks (they use your charisma to hit, you have proficiency, you don’t add charisma to damage unless you have that invocation).
The weapon itself takes 1 hand and has no tags (so you need Two Weapon Fighting to dual wield, etc).
Scavenging Blade. As a reaction to an enemy you threaten dying, you may strike the enemy dying with your blade. You (also) count as having killed the foe for the purpose of triggering any abilities which key off of that.
Eldritch Blast damage type rewrite
Re: EB and dealing force damage. I’m not ready to do this yet, but I _might_ flavor the damage by patron, with a choice of types (changeable each time you cast the spell), which emulates the irresistability of force:
Fiend: Fire or Necrotic
Fey: Poison or Piercing (counts as magic)
Great Old One: Psychic or Radiant