How a stronger Falklands defense changes invasion

How much more would Argentina need if the Falklands had a stronger air base and naval presence?

A great deal more; an on-station submarine alone could make the amphibious plan unworkable.

An earlier deterrent deployment used a submarine, frigate, and tanker. That small force had already demonstrated that an Argentine plan could be checked without a full fleet commitment. A submarine already on station could threaten the landing ships carrying the invasion force and make the amphibious plan unworkable. A modern-sized island air and naval base would raise the requirement still further by forcing Argentina to assemble a much larger operation before landing.