For things like this the stat I like to look at is the percentage of a player's shots that come from each distance range (0-3, 3-10, 10-16, 16-3P, 3P)
Vassell has only played 173 games but that should be enough for this stat to be useful. For his career 12.5% of his shots are long twos (16-3P) and 47.8% of his shots are threes.
DeRozan, by contrast, has 28.8% of his career shots as long twos and 9.4% as threes. He shot fewer long twos as a Spur but still at a far higher clip than Vassell.
https://www.basketball-reference.com....html#shooting
https://www.basketball-reference.com/players/d/derozde01.html#shooting
They have similar TS% stats for their careers (0.543 Vassell, 0.553 DeRozan) but Vassell has some room to improve seeing as he's only 23.