Could Sunderland flying boats save Force Z?

What is the theory behind a heavily armed Sunderland saving Force Z?

The theory is that a Sunderland's guns could disrupt attackers operating under tight fuel and defensive-armament constraints.

The proposed Sunderland patrol over Force Z depends on the conditions assigned to the Japanese attackers. They are described as short of fuel and having sacrificed defensive guns to achieve the required range. On those assumptions, a heavily armed Sunderland is considered capable of driving them off. The proposal rests on those claimed constraints and does not establish that the ships would certainly have survived.