I have to agree
I would bet that it's not a matter of extract versus grain but rather all the steps taken and not taken. Aside from all grain providing more flexibility in recipe tweaking and the enjoyment many in the hobby have planning a brew, I have to believe that an extract brewer can dial in a brew on level with the best all grain brewer as pointed out in the above post regarding award winning extracts.
Reading this thread about twang is interesting since no one have definitively posted on the so called twang but rather second hand anecdotes. hmmm.
I would gather getting old can of extract would be no different than stale malt grains also sitting around at the LHBS. I think if you were buying quality ingredients, good is good.
Have I not posted a first-hand account in this thread? Short version: I used to do partial mash brewing about 25 years ago. I got a good deal on a 30 pound jug of light LME; I'd use about 3 pounds per batch and I didn't brew that often. My beers started tasting "twangy", and I thought it was the table sugar I was using for bottle priming. In retrospect, the LME was just getting staler and staler because I wasn't using it up fast enough. I still have a couple of pounds of that LME in my deep freezer; it is dark like molasses now, so proper storage didn't help it just maybe slowed down the degradation.
Grain stays fresh for years if it's stored reasonably. So does DME. LME does not. When you buy a can of LME you don't know how fresh it is or how it has been stored. (it might be fine) When you buy grain or DME, it doesn't matter so much.
Extract beer can be just as good or better than all-grain. There's nothing wrong with or particularly inferior about the process. But that's seldom the case, whether due to the inexperience of the brewer or the quality of the ingredients, or a little of both.