if you start tracking reps and weight, i guarantee you will loose interest fast. while tracking might certainly be useful for muscle building, gmb.io has a different approach and focuses on movements that are safe and help you in real life (mobilise wrist / shoulders, prevent back pain improve posture etc). A lot can be done without fancy equipment.
But when I go to the gym once per week, and do 10 different exercises with weights or machines, I want to know what weight I used last time so I can start there (or just above it) again. Maybe you have the memory of an elephant.
Or Maybe you don’t care if you spend 2 minutes at every machine first figuring out what weight feels like just enough, not too much or too little, before doing 3 sets? Enjoy that. But I don’t want to do that. Every. Single. Time i go to the gym. And there’s no way to see my progress?
Not the parent, but I don’t think they are arguing against tracking weights when weight lifting so much as they are arguing against “traditional” weight lifting routines in general.
I have not tried gmb.io, but looks like progression in that program involves moving onto more difficult movements rather than increasing weight.