Agreed. If you look at the rule book update PDFs, the way Guardian Generators are explained lays things out more clearly:
• Against Gunnery Attacks, AA and CC, a roll of 4 or 5 results in a success
which cancels one hit against this model.
• Against Rockets and Torpedoes, a roll of 5 results in a success which
cancels one hit against this model.
• A roll of 6 always results in a success which cancels two hits against this
model.
Since a Guardian Generator provides Shield dice, this would be the same way shields are supposed to work.