Stats don't always tell the whole story, but in this case, they clearly show that Dyson was the more productive player across the board, and had a larger role on his teams.
Dyson averaged more points, rebounds, assists, steals, and blocks in his career despite playing alongside more talented rosters.
Rodney is the superior 3-point shooter. Dyson was better everywhere else, especially with the ball in his hands. Dyson was a great slasher, never tallying fewer than 100 FTA in a season. Rodney has never eclipsed that mark. Dyson's 28.1 AST% as a senior is nearly double Purvis' career high (14.6% last year).
Sure, Dyson's FG% is lower and TOs higher, but that can largely be attributed to the fact that his usage rate was substantially higher. Dyson was often the man on his teams, whereas Purvis has been limited to a more complementary role because he lacks the handle/playmaking ability to be a go-to guy.
Frankly, this really isn't much of a debate. The "eye test" already made it obvious enough that Dyson was the more talented player, but the stats just further demonstrate that he was a more well-rounded, productive player than Purvis.
By all accounts Rodney is a great guy, and has been a good ambassador for our program. But he just flat out is not as good as Dyson was.