This is kind of a silly thread. Tank is a solid player, but he is not at the level Heyward is, nor does he have that kind of potential.
Especially when you factor in Heyward is a plus defender with a plus arm and runs very well. Tank has a cannon for an arm, but he is simply servicable (overstatement?) in LF.
If GM's were given a chance to draft their teams from scratch, Heyward would go in the top 3 rounds, likely in the top 50 picks. Tank might be a top 10 round pick, but thats a coinflip.