You say blithely say "The offense just needed to score 4+ runs...", like that's the easiest thing in the world to do....something that teams rountinely do regularly, and that is simply not the case.
Scoring 4+ runs in 6 innings is a rate of 6+, or 7, runs per game, and that doesn't happen all that often.
I remember Bill James did a study once where he looked at each team's W-L record at different levels of runs scored.
Like when a team scored 0, then obviously their W-L record would be something like 0 and whatever.
In games in which they scored 1 run, it would be something like, I dunno 2-15 or so.
When scoring 3 runs, maybe they were like 10-15.
The more runs a team scores, of course, the greater their chances are of winning, and in this study I remember that the point at which a team had a better than .500 record was at like 5 runs per game.
The inverse of all of this, naturally, was exactly the same.
When a team allowed 0 runs, they were like 10-0 or 12-0.
In games in which they allowed 1 run, they were maybe like 15-1.
And so on.
The point at which the reached .500 was the same also.
Allowing 5 RPG, a team's record was always under .500, and allowing 6 runs per game it was even worse.
Maybe not a losing percentage of .750, but certainly one in the 60%+ range.
Anyway....
I took a look at all the games so far this season in which a team allowed (or scored) exactly 6 runs (it only took a few minutes because there haven't been that many games yet).
So far there have been 30 such games, and teams allowing 6 runs have a record of 12-18 so far, for a winning percentage of .400
Also, what you keep overlooking is the fact that in order to avoid a loss when allowing 6 runs, the pitcher's team has to score at least 7, and that just doesn't happen very often.
I took a look at the score of every game so far this season, and in the 137 games involving 274 teams, one team scored 7 or more runs only 82 times, or 29.9%.
What I’m trying to convince you of here is that when allowing 4 runs in 6 innings, a SP does not give his team a very good chance to win.
Even baseball writers, statisticians, etc., in their what I believe to be a very liberal definition of what they call a "quality start" would not include Zambrano's effort yesterday as such.
But thanks for giving me a subject to do a thousand+ words worth of comments on. :p
