Except the weight differences. HS shot out is 50% heavier than MS shot put.
Exactly this... And the Middle Schoolers throw the same size Discus as the HS Girls. The HS Boys Disc is much bigger.
Having said that, 170'0 in the Discus puts him as the 4th best MS Discus Thrower in the Country last Spring (based on the 2 most reliable websites I know of for Track Stats)... And one of them in front of him is Nixa, Missouri's Jackson Cantwell, the son of former Olympic Silver Medalist in the Shot Put, Christian Cantwell.
Epenesa's Shot Put puts him 19th in Country for all Middle Schoolers (Cantwell was 4th in the Shot).