"Electricity has a velocity (that is) as high as light’s (is)"

This answer ignores the physics implied by the sentences and focuses only on the English content.

In linguistics, ellipsis (from the Greek: ἔλλειψις, élleipsis, "omission") or elliptical construction refers to the omission, from a clause, of one or more words that are nevertheless understood in the context of the remaining elements. - wikipedia

Consider the sentences as elliptical constructions. Here are the sentences with plausible suggestions (in italics) for the 'omitted' words:

1a. Electricity has a velocity (that is) as high as light's velocity.

2a. Electricity has a velocity (that is) as high as light’s velocity is high.

Your question is whether your #2 sentence is erroneous. As the above demonstrates, the sentence is grammatically sound because it provides enough context to fill in the 'missing' terms.

I think you would come across much more clearly, if you instead structure this as "Electricity travels at the speed of light". The term velocity gets in the way of clarity in my opinion. This is particularly the case if your intended audience includes people who are not physicists or engineers.

By definition, velocity is a physical vector quantity; both magnitude and direction are needed to define it. But electricity in the real world is often transmitted along distribution networks with junctions. Therefore not all electricity travels in a straight line. So the concept of velocity perhaps clouds the central concept that you want to express.

The standard way of expressing this idea, at least in BrE, would be "Electricity has a velocity as high as that of light".