This is false. Breweries that make great beer have no problem selling out of their beer when they only sell packaged beer at the brewery. Examples include Tree House, Trillium, Hill Farmstead, Other Half, LIC Beer Project, Interboro, Night Shift (who actually own a distribution company now, but they sell out of new releases at the brewery within a day or 2), Monkish, Cellarmaker, the Veil, and many more in pretty much any major city that you can think of. Hell, Boston and New York have a half dozen each and new breweries are still popping up that are selling out of beer without distributing.
I agree that the 3 tier system is stupid, but breweries have proven over the past decade that they can scale up to 10k+ barrels per year without distributing a single thing.