Balancing Eldritch Blast against other Cantrips for Warlocks in 5.5e

Hey everyone,

I'm running into trouble with the modern rules, as they are indicating that WOTC is trying to open up options for warlocks in regards to their Eldritch Blast choices; however WOTC seems to not be balancing the performance. Currently I'm trying to understand the following example:

Both Warlocks have taken Agonizing Blast and Repelling Blast, both warlocks have 20 (+5) CHA score.

• Assuming hit: Warlock A casts Poison Spray. Warlock A, at level 20, would get 4d12 with a total 10ft knock back and +5 damage added from the CHA modifier.
• Assuming hit: Warlock B casts Eldritch Blast. Warlock B, at level 20, would get 4d10 with a total 40ft of knock back and a +20 damage added from the CHA modifier. While also being able to divide the knock back between 4 targets.

Warlock A would require taking the Mother of Sorrows subclass to overcome resistance/immunity to Poison (as Poison is a fairly common resistance), Warlock B would not have to worry about resistance as Force damage is the least resisted damage (likelihood is approximately <= 5%) type and could choose any subclass. 

RAW, it seems that there is no way WOTC can balance Eldritch Blast against any of the other cantrips, even though they're opening up Eldritch Invocations to allow the warlock to choose any cantrip. As a DM how do I make a game where my warlocks feel they are able to choose cantrips that are not Eldritch Blast without feeling like they made the "wrong" choice?

A Monte Carlos simulation run tells me the following:

• "Poison Spray can be expected to do between 29 and 32 total damage on hit 95%+ of the time, with a 10ft knockback on up to 1 target."
• "Eldritch Blast can be expected to do between 40 and 43 total damage on hit 95%+ of the time, with a 40ft knockback divided between 4 targets in 10ft increments."
  • "Assuming hit: An individual hit from Eldritch Blast will do 10 to 10 damage 95% of the time."

I am also working on adjusting my code to include "chance to hit", but I assume Eldritch Blast with it's 4x chance to hit is going to have a much higher likelihood to hit than the 1x chance Poison Spray gets.

Code used to simulate rolls (R 4.6.1): https://docs.google.com/document/d/1awcFtrJlgWidL-ud1D9atcT83O4Z4ntE1JhUXjnaEiU/edit?usp=sharing