I'm sure that makes sense if you just fall off the deck in normal weather. I just finished the Fastnet book and they described guys being caught in a wave of green water washing over their boat sounding like a freight train and grabbing guys, binnacles and masts and clearing the deck.
So if someone prefers to use a 2" webbing or a spectra core I personally wouldn't argue with them. I've never experienced force 10+ conditions but I'm betting that the force on a jack line in the right conditions could be significantly more than a 15' fall would produce. If you have a half a ton of water in your pocket it has to make a difference.
But for most of us most of the time anything is better than nothing.
Thinking about my answer later, yes it is possible depending upon the circumstances, that a larger wave washing over a deck, hitting you and you falling could be harder on gear than a rock climber falling say X feet! Not sure what X is, but I would be willing to swag that BOTH sports, could have higher forces than the other, depending upon "what" circumstances you are trying to compare.
With that in mind tho, "WE" as owner operators of our boats, need to know what type of seas, wave action etc we could have as worst conditions in the area we sail. Then if we go to an area with a higher extreme of wave/fall potential, we need to make sure the appropriate gear is up to the task.
So for me in Puget Sound, I would be surprised if one has to worry about the wave factor as compared to say a Volvo 70 or open 60 crew/operator etc in those boats, with speeds in the teens to 20's, even bursts into the 30 knot range, and waves crashing over you. ANy one whom thinks the safety gear for both options needs to be of equal strength to function is probably off base a bit. I could be plenty safe with lighter gear in my worst conditions vs a V70 is their worst conditions.
Like wise climbing, climb a local rock, it is different than climbing Mt Everest. While the gear may look the same, one will need to have appropriate gear for the issues involved.
But for most of use doing coastal cruising, and trying to stay on a boat with lost footing, a lighter wt webbing will probably work just fine, if it has a reasonable breaking strength