To be fair to Beane, those speedy receivers are gone in the top half of the draft and that is not where we were pickig the past five years. The other speedy receivers that go in the 4th and 5th rounds are 'flyers' taken on one-trick ponies. There is a rare chance that they become superstars like a Tyreek Hill; but the odds are against it.
The only mistake Beane may have made is swapping picking McConkey vs Coleman. It is somewhat a wash as both are inconsistent at best with McConkey being slightly better than Coleman (For every McConkey highlight reel, one can find a similar Coleman highlight reel).