Win,
1.
If you think you go further with a young, inexperienced starter at quarterback rather than your veteran, you make that decision before the season begins.
The following were rookies or in their second year and were started mid-way through the year: Montana, Bradshaw, Unitas, Dan Fouts, Tarkenton. But why would a veteran who is playing poorly every 3rd or 4th game be less likely to play poorly than a young guy who plays badly every 3rd or 4th game?
2. Last night was in a driving rain. Alex has been awful in rain, too. He did not play very well against the Giants in the rain at home in the playoffs last year. I really don't know where you got the "Kap choked against big competition in college" line. They were 13-1 his senior year and beat Boise State (#3 at the time) and won their bowl game. They averaged 41 points/game.
3. Of the 157 given up in 7 games, 42 were last night, 31 in the second half of the Patriots game. (Also many of them after Justin Smith went down.) The 4 starts before that: 7, 21, 16, 13. And the defense under Alex's watch had to play the mighty Jets, Bills, and Cardinals. (When we played the Packers we gave up 22.)
4. Coaches don't switch QBs in the middle of a game unless the guy has been terrible for weeks, not just one bad game. You are talking about a guy who just beat the Patriots in December! Why would you pull a 4-1 quarterback with one bad half? Alex is "battle-hardened by post-season play"? Two games. In one he played awesome (and the only big comeback I recall; quite frequently he brought the team nearly back). In the other he was average. We aren't talking one of the Mannings or Roethlisberger.

You are saying the rushing yardage is down when you take out Kap's runs. But Kap's runs were mostly designed. They weren't scrambles. Until last night, the four previous games we rushed for 144, 148, 155, 180. All that means is that the production was distributed differently. My response to that is, "Why cares?" You are also forgetting that Hunter is hurt. As much as we hope he will develop, James is (not now) the runner Hunter was (34 ypg). So Hunter's production is being replaced by Kap's. In our 4 wins under Kap, Gore's numbers have been pretty consistent to what they were under Alex. Over 4 ypc, 16-20 carries per game, yardage in the 80s.

I just think judging a quarterback--any quarterback--on a game played in heavy rain against the #1 defense in the league and one of the hottest teams in the league is pretty unreasonable, especially when that quarterback has beaten the toughest December team in the league for years and the #2 defense in points allowed (Chicago). If we did that, we would be benching Eli Manning (two weeks in a row of poor play), Drew Brees for the game against us (3 picks at home), and Rodgers for his game against the Giants. You have to look at the overall body of work. And Kap's overall play for 6 weeks has in general been quite good.