The better fencers in pentathlon are national- to international-quality fencers. The current men’s world champion, who is 37 years old, has also been national champion in epee fencing (not pentathlon, this is straight fencing) in Hungary, which is one of the most competitive countries in the world for fencing.
For running, ‘elite high schoolers’ means really elite. As in, the best going on to D1 scholarships. There are pentathletes who compete at a very high level in running, including one Olympic medalist who competed at world championships (in track) in a relay.
The best swimmers are people who’ve been just below national team standard. When you leave full-time swimming - which is a total beast of a sport with high-volume training - your times will slow down because you’re no longer swimming 10k/day.
When the shooting was static shooting (10m air pistol), pentathletes were often national or international class shooters.
‘Elite high schoolers’ sells pentathletes a bit short. The top athletes are truly outstanding athletes in every discipline.
In the US, people often come to pentathlon after being successful in other sports like D1 college swimming or running. They think pentathlon is a ‘shortcut’ to the Olympics. Then they go to their first international competition and get their ass resoundingly kicked.
If anyone has questions on training, please ask. It’s interesting to see people making speculations but it might be easier just to ask for the facts.