He is nothing like Siakim....Yeah, we're going to disagree again, pretty much on all of this. GG is actually a switchable defender and can guard 2-4. His team at SC has been playing a 1-3-1 zone a lot, which hides players' defensive abilities. GG makes limited effort to guard beyond his immediate space, but he's got both the tools and advanced timing to defend. He's positionally pretty sound and averages 1.9 stocks per 36 mins. He's also rebounding well, pulling 7 boards per 36 mins, with is the same as Jeff Green as a junior at Georgetown.
GG scores at three levels with little-to-no help from his teammates and despite the fact that he often has to beat multiple defenders. He takes really difficult shots with small time/space windows to get shots off. He's not getting open space unless he steps out to 25+ feet. Even so, his 3pt percentage is currently 35%, which is on par with Tatum at Duke.
Shabazz Muhammad was successful in his HS class largely because he was 2 years older than everyone else. He played bully ball that worked at the HS and somewhat at the college level, but didn't translate to the NBA. Ultimately, his attitude also hurt his NBA career. GG is closer to Harry Giles of his HS class. He's got a high offensive skill level for his size and age. The hope is that he'll fill out to a legit 6'9 / 225 lbs with the ability to create space and open looks for himself within NBA offensive concepts
GG's ceiling is like a shiftier, slightly bouncier version of Siakam, but with more in-between game, which would make him an All Star-caliber player.
Brandon Miller is closer to Paul George than GG is to Pascal Siakim.