This expectation that all first rounders have to be great from day one is... ludicrous.
Sure, it'd be nice, but not all positions are created equally, indeed, some positions are widely known to take a couple of years to really blossom-- tight end, quarterback, and cornerback, in particular have this reputation.
Last year, Mr. Grier took three players in the first round who all shared one attribute in common... they all were said to have extremely high ceilings, but might take a couple of years to really excel.
This is taking home run swings and trying to find elite talent, and this beats the Hell out of taking 5th year seniors who are maxed out.