Yeah, Sagan is extremely impressive. And is IS natural talent, because he certainly does NOT have this substances/blood treatment methods that others don´t have.
Repoxygen currently seems to be the maximum, the most effective substance endurance athetes could use. Given the fact he had access to this, he should already have had access in 2010, when he turned pro and was already really strong. Two years have passed, and if he should have had access in 2010, others surely will have in 2012 even more. So this can´t be the reason.
Sagan is extremely gifted. Rebellin 2004, Gilbert 2011, Bettini, Valverde - he seems to reach their level within the next 1-2 years. And he already has the consistancy of these top riders, performing from February to autumn.
He should be able to take Green in the Tour some day, become World Champion, Olympic Gold Medal Winner, and win all the five mouments.
Since his first pro races in January 2010, Tour Down Under, he has been just impressive.