Actually Tjark’s take on Tatum is a fairly common one in NBA circles. SI’s NBA commentators and podcasters raised similar questions, while also citing that a lot of people in Vegas are mixed on Tatum, despite a lot of the praise by the Boston media.
Also the AAU rationale is a pretty strange one. This year was uniquely talented at the PG position, with 6 of the top 10 prospects coming into this year as guards. This is somewhat unusual compared to past seasons. For example only 2 guards are in the top 10 prospects for 2017 (top prospects are Porter, Ayton and Bamba), in 2015 3 of top 10 prospects were guards (top prospect was Ben Simmons). And honestly this is one few years that these top guard prospects all actually had good college seasons. The likeliest conclusion is just that this season is somewhat of an outlier with really good guards, not just that its AAU ball.