This...
A lot of these people are incredibly strong, with horrific flexibility and true endurance. They can do 100 pullups, but I rarely run and can beat many of them in a 5k...or play pickup basketball for 90 minutes and they're asking to be subbed out after 15 minuts of running up dna down the court. They train for burst energy rather than endurance. Why most of them are terrible boxers as well. They don't have the endurance for shit like open water swims.
I trained for triathlons for a while. I quit because...while I'm a good swimmer, I'm not built for distance/open water swimming. I have a long torso and long arms, but I also used to squat 650 lbs, so I have a huge ass. Took a lot of extra stamina just to keep my body horizontal in the water, and that didn't equate to me being able to keep good pace for long enough. And I hated swimming open water to boot.
These folks shouldn't be swimming more than 250 meters tops, and damned sure shouldn't be doing it after they run.