They're the same height, but Sheppard's 25% assist rate is the main thing separating him from McCain (12%) in my mind, as 6-3 should be workable as a starting PG in the NBA but probably not as a pure SG like McCain is trending toward.
They're both at 90% FT, and I assume their 2pt% and 3pt% will converge as the season goes along. Kentucky has somehow played a significantly easier schedule than Duke has per sports-reference SOS, Sheppard's 56% 3pt is highly unlikely to be sustainable, and McCain's 2pt% is catching up now that he's over whatever 2pt funk he was in to start the season.
Another big difference is Sheppard's apparent defensive activity. 5.6% steal rate and 3.9% block rate is borderline unicornish for his size, whereas McCain's defensive numbers range from pedestrian to bad all-around.
Will be interesting to see if McCain makes any strides in passing and defense this season. Coming in at #13 on 247 composite versus Sheppard's #47 is confusing given what they've shown.