You're underestimating how much Santana is better than your average #1 pitcher.
For the following aces, PECOTA projects:
Sabathia 15 Wins, 215 IP, 3.51 ERA, 1.22 WHIP, 179 K's
Beckett 14 Wins, 205 IP, 3.68 ERA, 1.22 WHIP, 176 K's
Bedard 13 Wins, 194 IP, 3.58 ERA, 1.27 WHIP, 196 K's
Peavy 15 Wins, 212 IP, 2.98 ERA, 1.13 WHIP, 223 K's
Webb 13 Wins, 200 IP, 3.38 ERA, 1.24 WHIP, 155 K's
Only Peavy comes close to Santana and I think Peavy should be drafted no later than mid-second round. The rest of the aces that you can get in round 4 are likely to produce much less than Santana. Now if you believe someone like Sabathia is going to repeat his Cy Young type year, I can see passing on Santana in the first.
"And so he spoke, and so he spoke, that lord of Castamere. But now the rains weep o'er his hall, with no one there to hear." - The Rains of Castamere