Maybe they aren't right on, but as a rough approximation -- certainly as a way to evaluate QBs against each other-- they work OK.
Vick is near the bottom of the NFL in every year he has played. He is one of the better running backs in the league, but that shouldn't be what an NFL QB does.
Your posts about Vick (terrible ratings, flawed style, poor quarterback) lead logically to the conclusion that the Falcons are winning in spite of Vick; unfortunately, the logic is tortured by your claim that the Falcons are a mediocre team.
Remember, we're talking about a competitive sport; hence, the notions of "good" and "bad" and "mediocre" are rendered relative by the fact of competition. If Vick is mediocre and the Falcons are mediocre, yet have amassed an overwhelmingly superior regular season record and are among the four teams left in the playoffs, one might conclude that the league itself, in whole, is bad; in order for the Falcons to have risen to "mediocre" status, they will have had to have risen above the "bad," as it is the only subjective designation above which the "mediocre" can rise. "The mediocre" resides, by definition, above "the bad" and below "the good." If the Falcons are merely mediocre, the rules of the NFL designate that there can only be the possibility of three "good" teams in the league this year, as the rules are structered so the best teams will usually rise to the level of the playoffs. If the Falcons are merely mediocre, every team not ascending to their status in the playoffs must either be "mediocre" or "bad" teams, and only three teams hold the possibility of being relatively "good"; of course, using this model, they could all be merely "mediocre."
But this cannot be. Since the nature of the quality of the participants in a sports league is determined by competition, the notions of "good," mediocre" and "bad" teams are derived from a subjective and comparative process. The Falcons must be better than at least one of the other teams making the playoffs this year, the Rams; and although their regular-season record was 8-8, they were among the best teams in the league. If A is better than B and B is better than C, then A is better than C. If A is the Falcons, B is the Rams and C is the other teams in the NFC minus Philadelphia, then the Falcons are better than the rest of the teams in the NFC minus Philadelphia, because this is how the postseason is structured.
So, we can rightly sat that we have the "best teams in the league" and the "worst teams in the league" and "everything in between." These designations make no sense if we separate them from notions of "good, mediocre and bad," because the nature of competition in a sports league introduces the notion of relativity giving rise to the commonly-held understandings of these terms.
Due to their regular-season record (especially in comparison to the records of the other teams in the NFC and their status as a participant in the NFC playoff game) any rational opinion of the NFC and the Falcons will entail the belief that they are, at least this year, a "good" team; they are not "mediocre," as they are one of four teams left in the playoffs. Therefore, if Michael Vick is a "mediocre" quarterback, it is the Falcons as a team who are winning in spite of his mediocrity, and this has been some incredible effort, as their record is outstanding by any measure.
Even this reasoning is preferable to your notion that both Vick and the Falcons are "mediocre," because these designations can't rationally co-exist considering their status this year. We have the fact of their record and their rise to the NFC Championship Game. You could believe that the Falcons are "good" and Vick is "mediocre" or that the Falcons are "good" and Vick is "bad" (in both cases with the Falcons winning in spite of him); you could believe that Vick is "good" and the Falcons are "mediocre" or that Vick is good and the Falcons are "bad" (in both cases with the Falcons winning due to Vick and in spite of his team); or you could believe that both Vick and the Falcons are "good" according to separate criteria. All of the above are possibilities. What isn't possible is for either the Falcons and Vick to be either both "mediocre" or "bad," because relative to the competition we see this as an impossibility. Somewhere and somehow one or the other, or both, must be measured as "good" relative to the competition; and "the competition" is the entire nature of the entire NFL.