I don't think you understand the use of the term unicorn in this context. A unicorn is a mythical creature, something that is rarely, if ever, seen. In that context, Allen Crabbe is the furthest thing in the NBA from a unicorn. As a 6'6" wing, he is the prototypical NBA 3 and D player. They are all the rage these days. It seems like every team (except BRK) has at least one, many teams have two, some teams even three. It seems the current recipe for success in today's NBA is a scoring PG paired with a 3 and D player at the SG and/or SF positions. In fact, that was exactly what we had with Wes and Nic the season before last.
That doesn't mean Crabbe isn't good. It doesn't mean he's not valuable. It just means he's not rare. He's not a potential unicorn.
How many teams have a guy 7'1" who is an elite level 3-point shooter that's big enough to effectively guard, and frustrate the shit out of, DaMarcus Cousins? Can you name one other player like that in the entire league? And by elite level 3-point shooter, I mean > .400 3FG%.
Of course, the reason Meyers is referred to as a potential unicorn is he has other holes in his game, but it's the potential to be something unique that gets people talking about him.
BNM