u/Afraid-Afternoon6403

I’ll preface this with, there is no objective data on what sport or cardio is the most demanding (as far as I could find.) Much of this discourse is likely just perceived effort, someone who hates cycling but likes swimming might find it easier to swim and vice versa.
I recently had a discussion with some friends about swimming vs cycling. My stance was swimming is the more demanding sport, he stated that cycling would be a more difficult sport due to the requirements of less body parts involved and how difficult it is to get your heart rate up into zone 4/5. I stated, I believed swimming to be the more difficult and/or more demanding sport as it’s more closely a full body activity, while managing your breathing and your form.
The resistance of water already being 800x that of air and this was on the basis of just pool swimming. Open water swimming is another beast to conquer, which I think is a step above the pool and puts a larger gap in physical fitness and skill on cycling.
Much of this topic is almost purely subjective, this just happens to be my stance, swimming is one of the most demanding, with cycling not being ranked above it.
I’d like to hear your thoughts and opinions whether to sway me or him.