No, they aren't. Jason Campbell is many times worse than Flacco despite their similar stats.
Stats that take into account factors not accounted in the regular stats, such as those by Football Outsiders, are better indicator, imo, even though the team factor in influence the stat is not completely accounted for; they don't say everything about a QB's play either, but they're more "complete".
FOOTBALL OUTSIDERS: Innovative Statistics, Intelligent Analysis | QUARTERBACKS 2009