So the kid is in his strength and adaptation period. He is in the gym and doing unstructured group rides. Ok. Not my favorite way of doing things but there are those that train this way. Power is basically just being recorded because he is not doing a thing with it. It is not altering his training whatsoever, unless his coach is giving him specific instructions on what to do in the group rides based on what he sees from the power data. We have no evidence of this.
Fatigue is being tracked by HR. Ok, but long term trends based on HR are just not accurate. They are fine for validating that your kid is tired but there are so many other factors that affect HR that I would not consider it reliable. So how are you tracking TSB and CTL during this period? One of the most valuable things about training with power is preventing overtrainng.
How is is he going to train during build? Is he going to continue the group ride thing or is he going to do intervals? If he is going to do intervals, how is he going to measure effort?
Again, I think either you are a poor communicator, or someone on your kids team has a severe lack of knowledge on how to train and race with power.