We're all excited by what Dak Prescott has shown this preseason and most of what we've read analyzing his play has been qualified with "it's preseason...teams aren't game-planning for him...vanilla defenses," which may all be true (to an extent), but are undercutting what Dak has done thus far.
First, the defensive schemes he's been facing are not that vanilla; he's not playing against defenses employing Senior Bowl schemes that can't blitz or are forced to run a 43. These teams are trying to get their personnel up-to-speed and comfortable with their own respective alignments and coverages so the notion of vanilla defenses is overstated.
Secondly, what's impressed me about Dak is the quality of throws he's been making. He's been hitting guys on the move, throwing to spots on deeper throws and carrying the safety/linebacker on certain coverages. That's impressive. What we've seen in previous years were guys like Dustin Vaughan become Checkdown Charlie and throwing to the easy read in the flat/comeback route.
Finally, if all these aspects brought up to temper the praise of Dak were true, we'd see a lot more rookie or young prospect QBs performing at a much higher level than they typically show.
Bottomline, I agree with being conservative with the praise, but I think there are very legitimate reasons to be excited at what Dak has shown.