Britain has much better strategic power projection capabilities than she had in 1982, but perhaps slightly inferior tactical power projection capabilities.
The islands could be reinforced heavily within the space of 24-48 hours by heavy airlift if neccessary thanks to RAF Mount Pleasant’s large and capable runway. It would be hellishly hard for them to take the islands.
On the other hand if they did, things might be more difficult, although not having fixed wing aircraft might not be as much of a handicap as it was in 1982. I’m not an expert by any means but the ‘Daring’ class destroyer is an extremely capable AA platform that would probably completely deny Argentina use of the air, whilst Apache gunships filled some of the gap by providing an air support role that the harriers would have done had we still had them. We also have SSNs with Tomohawk cruise missiles, which means that the Royal Navy can strike anywhere the Falklands or even mainland Argentina at will with virtual impunity, unlike with the extremely tenuous ‘Black Buck’ Vulcan bomber missions we relied on back in ‘82.
Basically, despite the loss of the harriers, a British task force would still have considerable anti-air and and strike capabilities that are probably even better overall than they were in 1982..
Counting on destroyers as your primary air defense umbrella is tenuous. The Apaches could provide the ground support, but in 82, they kept the Argentine air force at bay, which still did a lot of damage. Without any fixed wing air craft. Let’s not forget that the UK ran out of missiles in Libya, and those things are not cheap to replenish. Also, Airlift can only move a fraction of the material that can be moved in the same time by sea lift. If Britain had to rely only on air to move the amount of men and materials necessary to fight an 82 style conflict they would be hard pressed. Their military sea lift capability would depend almost solely on borrowed civilian shipping. Argentina’s a basket case, and I’m sure the U.K. would prevail, but mainly because Argentina has disarmed to a greater extent than the British have.