Warren is spectacular going coast to coast off the dribble. He builds up a lot of speed and can maneuver around defenders. Superficially, he doesn't look like a good athlete but he really is. You can't play like he does in the open court and not be a good athlete. The 15 pounds he's lost since last season has made him quicker and faster. Even so, he's still a big bodied small forward. The shape of his body is similar to Pierce's--wide shoulders, an absence of NBA-type muscle tone--but his arms aren't nearly as long although he may be an inch taller.
The only modern wing I can think of with a similar shot repertoire and volume from 3-8 feet is Chris Douglas-Roberts but Warren is taller, much stronger and a better athlete. It's silly to compare him to a hall of famer but he has some shades of pre-ACL Bernard King to his game.