Overrated depends on severity. If someone says he's the 2nd best QB all time and you have the two hours and statistics to convince that someone that he's only the 3rd best QB all time, then there's probably been a whole lot of time wasted. If someone believes that Favre was not only the greatest QB ever but the greatest player period, who single handedly saved franchises and instantly turned the '86 Packers into the '96 Packers all by himself and he's on an existential plane all his own above the mere mortals like the Montana's, Brady's, and Graham's of NFL history, while actually being a Jim Kelly caliber QB around the 17th best all time, and perhaps around the 85th best player ever, then maybe time isn't being wasted. Because it's those former people who have formed their cult around Favre based on erroneous assessments (which they are welcome to in the quiet conduct of their lives like any religion) and they get up into other peoples' grill ("you're not a real Packer fan if you don't like Favre anymore") that corrections to the severity of their overrating are necessary. They use their massive overrating to either refuse to acknowledge Favre's dingleberriness beginning in at least 2005, or if they do acknowledge his behavior, he was entitled to act that way. Even as everything Favre whined about (with perhaps the exception of Wahle for one season) was proven wrong, Favre was STILL due all and everything he wanted and the Packers were wrong in denying him his mandates, because he "saved franchises", "when your three time MVP tells you to hop, you ask how high", yada yada yada...
To keep it simple, Favre is overrated because there are plenty of people wowwed by gross-weight statistics rather than detecting, era for era, when a QB played very much above average. The last four record holders and the only current QB pushing at records (Unitas, Tarkenton, Marino, Favre, and P Manning) have only four championships between them, covering 88 NFL seasons over 57 years. Meanwhile, the QB's who measure the highest in AY/A (adjusted yards per attempt, which simply combines elements of QB rating efficiency with a factor for risk taken) have eleven. A little broader, the top ten QB's in yards thrown have a total of eight championships versus the top ten in AY/A have twenty-two (twenty-eight if you include the six that were won in "feeder leagues" that put teams into the NFL (AAFL and AFL)). The top ten QB's are those who took risks and succeeded more often and won championships. The second ten are made up QB's who took risks and didn't succeed as often, and they kept plugging away at more championships and failing but gathering buckets of statistics along the way. Does it take away the fact that they are HoFer's? No, just that when ordering HoFer's, a lot of people default to the shiny tinsel of gross-weight statistics instead of pound for pound quality of output. And therefore the statistic gathering guys tend to be overrated. Favre falls into that category. Then take that tendency to overrate statistic gathering guys and add in a whole extra narrative of "saving franchises" and a psychosis is born.
Having said all this, I'd easily take a Jim Kelly caliber guy over a randomly picked QB any day. I'm not trying to downplay Favre, his talent, and his contribution to the success of my favorite team. All I wanted in the late 70's was my team to be the Cowboys. And they effectively did (at least as close as a team could get in the post '92 free agency/salary cap NFL) and Favre had a lot to do with it. But a boatload of other people had a hand in it as well. And I'd be more than happy to embrace Favre if he hadn't been such a *********** starting in 2005. Too much whining and too much sulking and too much disruptiveness, and ultimately too much revenge seeking, for my tastes.