This is exactly my perspective on the competitive/ casual dichotomy that everyone seems keen on using. Competitiveness is an attribute of the player. I can run a $1000 highly tuned Memnarch deck, but it's not competitive unless I actively choose to do broken stuff. I could just as well choose sub-optimal plays and just 'have fun' with the game rather than aiming for total game control turn 5. I don't think it is competitive unless i always make the 'best possible move' every turn. Sometimes a guy can just wing it, and tutor for a janky fun thing instead of a combo.

Putting the best cards for a certain role is the most logical thing to do, but there is difference between using the deck to its maximal potential each game and being a functional, social being who can take hints from context. I think it's fair to have an 'optimal' build, because (for some people) you never know who or what you will play against next. You can always toss the ball underhand once in a while, but it's much harder to go the other direction. For example, in my Scion deck, I won't use a turn 5 [[Atarka, World Render]] + [[Moltensteel Dragon]] combo on my little brother if he's playing one of his low power builds.

I think that is where the 'middle ground' lies in EDH - The middle ground exists where a person responds in kind to a deck. Don't boardwipe a janky tribal deck unless they are actually a threat, just because you drew the card. Try not to combo out unreasonably early if its clear that other decks are taking much longer to get online. It's like letting a NFL player play with a group of neighborhood kids. He's not gonna pummel them for fun, he'll pull some punches like a normal, empathetic human being.

TL:DR - I agree that there are no competitive decks, only competitive attitudes. I disagree on the middleground, as I think there are lots of opportunities to evaluate the choices over the course of a game.