I initially thought Agonizing Blast made eldritch blast too strong. After a lot of research and discussion, I decided that it doesn't. In fact, the way the warlock is designed it is important that they have such a high damage output. With it, warlock is a fairly balanced class. If you nerf it, the class can fall to a subpar status.
Also, it is worth noting that each blast does not hit at the same time. I think that was clarified in a tweet.
I agree with everything except the last bit.
Going down that route is a rabbit hole that doesn't lead anywhere.
Asking whether a spell like Eldritch Blast (or Magic Missile etc) hits simultaneously or not is a fallacy, because it suggests the outcome is different depending on the answer. It is not.
If all four blasts hit the same target, it takes four times the damage, four times the Charisma adder, and four times the push effect. Regardless of whether you apply them all at once or one at a time.
This is because it is only one single casting, and all the rules for spells not stacking talk about multiple spells (and not damage, and only conditions etc).
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The sorcerer affinity is something
completely different. It is a feature that adds a bit of damage to some of your spells.
It is not meant to add four times as much benefit for one spell (Scorching Ray) than another (Firebolt) or a third (Fireball). In all cases, this feature adds only its ability modifier once. Equally to all spells.
This has
nothing to do with how spells stack and does not stack.
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The poster is comparing apples and oranges.
The Warlock invocations
change a spell, and only one spell at that. Its designer knows the spell in question, and I feel it is reasonable to assume he or she knew that you gain additional blasts as you rise in level. If the intent was to only give the riders to one/the first blast, the burden of proof would have to lie on writing that clearly.
The Sorcerer feature
add to spells, and many different spells at that. Its designer treat all spells equally (as per clarified intent). Something very reasonable, and not something that reasonably needed to be spelled out.
There is
no reason they should or must work alike.
Remember, 5th edition uses "natural language", not lawyer-speak. That is why it is reasonable to evaluate a paragraph using fuzzy subjective language such as "reasonable" above. (Trying to rules-lawyer a specific outcome will get you nowhere. Or, rather,
I am rules-lawyering an outcome. I am just using the new toolbox and not the old obsolete one

)