The most common comparison if Langford hits his potential is DeRozen, but that's only because Romeo didn't shoot well from 3P in college. But if you include becoming a league average 3P shooter, you're going to have an All-Star.
At IU, Langford shot 66% on shots in the paint, which when I read this is usually prefaced by the word "ridiculous." But the NBA.com article linked below also said that "he scored "a tremendous
1.346 points per finishing opportunity in the half court [87th percentile]" and that's when Romeo was the focus of every defense plus he had the hand injury.
This
article from a Miami Heat blogger has a bunch of fun stats, including that he was in the 98th percentile when finishing off the high PnR.
DeRozen with a 3P shot. Whoa.
Some more stats here:
https://stats.nba.com/articles/2019-nba-draft-profile-romeo-langford/