Once you fix the obvious typo there, it says "GW is [...] _as_ valid and important measurement as the amount of energy it stores"

Which is entirely true... Both the overall capacity, and the rate at which it can deliver power are critical metrics for an energy storage system.

You're reading it like this:

> GW is [...] a [..] measurement as the amount of energy it stores.

Which doesn't parse. If the text read "of" instead of "as", I might agree with you. As it stands, it doesn't correctly parse either way. Given the full context of the statement, the more likely original intention was that:

> GW is [...] just a[s] valid and important [a] measurement as the amount of energy it stores.