I would put an average homebrew up against most commercial stuff.
I don't think you hang out with average home brewers.
Seriously, the statistic the AHA uses is one million people per year brew at least once. If you only brew once a year you can't really expect to make *great* beer. So I'd wager half of all homebrew is downright bad - these are the people who get discouraged and never brew again. Then there are the people who brew like I play golf; every third shot looks good enough that I'm encouraged to try again. And then you get to the minority (it can't possibly be more than 50,000 or so) who are consistently making *great* beer.
In pro brewing, you have essentially the same division, albeit hopefully without the people who brew once and give up. But in the brewing industry the ratio is flipped - 93% of the beers on the market are adjunct lagers that are, technically, flawless. Granted, there are a lot of pro brewers who aren't consistently making great beer, but they're a minority, and by and large the market does a pretty good job of shutting them down.
So while the absolute best (and worst) beers could well be homebrews, I don't think an average homebrew would stack up very well.