Good NRL players are very rare. I don't know for sure how many Australian schoolboys captains have made it to NRL but there aren't many, 2 or 3 maybe. Gun juniors don't always make NRL. There's a level of physicality required to make it and I don't think Galvin has that.
The better players have either size, speed or power. Skill players who rely more on smarts still need to have a physical advantage. For example, Cleary is 95kg's, quick off the mark. Moses is a smaller guy but very fast, particularly off the mark. Galvin has no speed, is a terrible defender and presents no physical threat. In fact, he is probably a target in defence, requiring a very good second rower inside him and a very good centre outside, which he may get at the dogs. Latu is fast, a very good defender, strong in taking on the line and has excellent draw and pass skills. Far superior to Galvin. If he stays fit, he is a great improvement on Galvin.