Well no shit he's gonna be pressured a lot, but all that shows is that the o-line needs to step it up. I'm sorry but "he's going to be pressured" is such a piss poor reason for an incoming QB to be doubted because EVERY QB is going to be pressured. It is his job to trust his o-line to hold the pocket long enough for him to make the play. You don't judge a wide-receiver for balls that don't get thrown to him, so why would you just a QB for a line that doesn't do their job to make you comfortable in the pocket?
OT: Here's to hoping KC goes after a QB this season. They have some holes to fill in their o-line(hey look at that), but they need a franchise QB to put behind that line and I'm honestly hoping after watching some of RGIII combine videos that Pioli will man up and make the trades to St. Louis for the pick to get him. That or as everyone doubts/questions perhaps a certain Manning could be doing the Tomahawk Chop this season. No matter if either RGIII or Peyton come to KC, the one thing I know is Cassel needs to begone.
A QB that has his ratings over three seasons that periodically span from sparingly amazing to generally abysmal is not the QB you want leading you team to after 19 seasons without a playoff win and 42 without a Superbowl.