Would your be able to see it as it is?
They aren't getting extra help. Their bodies are more developed so they cope with extra training. And soooooo many age groupers who excel at 13/14 due to early puberty are dropping out by 16.
Those who started to achieve and increase training at a later age are still going at college age.
I've seen it sooooo many times. 13/14 yo with stubble and who look 18 breaking county and regional records - winning national medals burn out. They don't get the same gains the age groupers are still getting because they hit the times the older age groupers are aiming for by 17/18 at 14! You cannot swim a 0 time. You can't always just keep getting faster and faster and getting those marginal gains requires more than squad swimming can offer lower club level.
Ds club offer those opportunities once you are performance squad and especially to those in national performance squad. These are the swimmers who have now got the mental resilience to cope with the training required to make marginal gains. They've got the engine - they've done the years of aerobic training you need. And just swimming set after set is no longer enough for them. It is enough for young age groupers who don't know what adult physicality they'll have and what type of swimmer they'll be.
His club have said their younger swimmers are no longer being allowed to pick their favourite and best strokes to race. They'll be told what they are racing and it won't be what they think (or maybe even want!). They need to be all rounders so when they are at the stage of specialising they have the foundation.
Ds is now specialising in 50 and 100 free. But he's 18. Even then he's changed his second stroke. 10 months ago it was back and now it's fly. Coach made him work at fly saying he thought ultimately he'd be stronger at it. It took 8 months for it to be better then his back!!!
The fact your ds cares and wants this is his biggest attribute.
And if his coach wants more ambitious goals encourage ds to go for it. I'd certainly say a medium term goal for him is a top 5 finish at OW nationals. He's proved he has the training ethic and ability to do that!