In Vintage the proper term is "unrestrict" a restricted card, not "unban."
Additionally, I elaborated on "unfun" a while ago. The standard is not whimsical:
Even if both players have access to a very good strategy, one player gets to use that strategy first in Magic. Unfortunately, one of the drawbacks of turn-based games is sometimes the fact that there are turns; one player gets to go, then the other. While in chess this advantage is relatively trifling, in Magic (and especially in Vintage), the advantage provided by going first cannot be underestimated. Even though one gives up card advantage by going first, players unanimously say "play" when posed with the question "Play or draw?" This is ultimately where the game can break down and the necessity (and, I believe, the philosophy) of the B/R becomes apparent.
The first turn win is not something that is valued by the Vintage community. This is because the player on the draw essentially gets no opportunity to win, or even play! Such wins are often attributed to luck (either by the opening seven or the roll), but they can also potentially be attributed to skill if a player comes up with an ingenious and consistent enough deck. However, even if such a deck required an incredible amount of skill to pilot, the Vintage community would most likely still find it unacceptable if it could win on turn one consistently. Furthermore, even if a player isn't winning on turn one, the player who goes first gets additional mana, an additional set of main phases, and an additional combat phase. This initial advantage persists throughout the game. So, in one respect, the B/R is about getting to turns two through five and beyond, if possible. By getting to the later turns, skill, rather than luck, is often allowed to determine the winner of the match. It is probably worth noting here that "skill" incorporates both play skill and deckbuilding skill (in case someone tries to make the distinction).
Ultimately, what I'm trying to get to is the idea that the B/R is trying to achieve fairness for the players involved. But how do you define that? I would suggest that pushing the game more toward skill and away from luck is how that is defined in Magic. That's really the whole point of playing the game: to determine a winner by skill rather than luck. Otherwise, whenever you win a tournament, your numbers just happened to come up for the Mox Lottery that day. Where's the glory in that? I think the ideas of "objectively overpowered" and the infamous "unfun" associated with Trinisphere fall into this category, pretty much no matter how you slice it. The above paragraph is what I think Mr. Forsythe meant about Trinisphere rather than the one word explanation that has now become irreparably associated with the card. In the DCI's opinion, Trinisphere pushed the game too far toward the Mox Lottery. Now whether that is true or not is certainly a topic for discussion, and reasonable minds can differ. For the record, though, I personally am of the opinion that Trinisphere belongs on the Restricted List for this reason. It's about "unfair", not "unfun."
Edit: Is the author of the article able to post in this forum?
