@
Arial Black I will continue consider 'instantaneous' to apply to the effects of the beams/the individual beams and not the whole time period of targeting/beam/damage/repeat. Nothing breaks for me with that interpretation.
In your own game you can do what you want, but as part of a rules debate,
why would you have us believe that 'duration' (which is defined as the period of time the entire spell effect exists) means something totally different for
eldritch blast? This is not four spells, each with an instantaneous duration! It is a single spell whose duration covers all four beams.
As for ready actions between spell attacks JC would allow them to trigger of individual attacks. I'm not a fan of that for spells, personally.
I will continue to not consider a readied dispel magic to be a viable replacement or even half power replacement for counterspell.
Correct. You cannot target the
casting of a spell (the VSM components) with
dispel magic because chanting words and gesturing are not magical effects, and the spell effect does not begin until the casting is finished, by which time it is too late to prevent the effect from starting (the duration beginning).
However, once the VSM components of
eldritch blast are completed, the spell effect (four beams of crackling energy streak towards opponents) then the spell effect does exist and may be targeted by a dispel,
if the spell effect's duration has not yet expired by the time the dispel goes off.
If the beams are effectively simultaneous, with no time to react until they all hit (which would be true for both caster and dispeller),
then the beams have come and gone so quickly that there is nothing to dispel.
But,
if there is enough time between beams for the caster to see what the first beam did before aiming the next,
then there is enough time for the dispeller to release his already cast
dispel magic. He has a valid target because the spell duration is still ongoing at that point; the spell duration (whether you call it 'instantaneous' or not) begins with the first beam and doesn't end until the last beam. Since it is dispelled after the first beam but before the second, EB is an existing spell at the time it is hit with the dispel.
I don't know
why JC wants it to work this way, but if the spell does work this way then the consequence is that it can be dispelled, contrary to what he wrote about instantaneous spells.