Free weights are vital for muscle strength, mass and edurance. That doesn't mean free weights take the place of your other activities such as skiing or mountain climbing. That doesn't mean that you cut out cardio, that's something else entirely, even though some people work on cardio in the gym along with strength training.
Free weights are also great for building the entire structure of your body. There is nothing which can stress the major muscles of the legs, bones and supporting muscle groups like throwing a huge weight on your shoulders and squatting that weight multiple times. Swimming, isometrics and all that other stuff won't do it. Machines also don't do this because you don't have weight to stabilize in both directions. The power move of the squat is to push upwards with your legs but you still have to lower that huge weight in an orderly down movement to start the exercise.