The average height of an NFL WR is 6'1⅞"
The average height of an NFL DB is 6'1¼"
Hardly a difference in the two.
But, let's pretend your incorrect assumption that most WRs are taller than most DBs were correct. Why would you believe that Boo being smaller than average DBs would be an effective defender against players you incorrectly assume are taller on average?
In other words, if Boo is 5'-10", isn't he at a disadvantage as a DB if the average WR is 6'2" when his position is responsible for making a play on the ball every time it's thrown his direction? Conversely, on offense, you get him the ball in uncontested situations (screens, jet sweeps, etc.) where his height is of no consequence and let him make plays with his athleticism.
The belief that WRs have to be 6'3"+ to be successful is antiquated thinking. I'm not necessarily attributing that belief to you, but it's a common misconception. The game is played in space, now, and diminutive WRs are everywhere on offense in college and the NFL.
Squirrel White was our best WR this year. He's 5'10". Luther Burden is 5'11", Ainias Smith is 5'10", Dayton Wade is 5'9". That's four of the top-10 SEC WRs in yardage this season.
I appreciate the discussion, and I realize I probably won't change your mind. I'm fine if Boo ends up being a DB, and like you, I just want him to be successful no matter where he plays.