I don't think the thought process of "we are playing like the top team in the east, imagine if Gordon weren't out," is not a complete context to the current play of the team. The obvious factors are Kyrie ballin out of his mind, Horford thriving off of having a shoot first PG that can consistently switch that shooting instinct off to get his big man tbe ball, Baynes showing up far beyond expectations (I called that he would be starting for us pre-season), and basically every other new player/rookie being solid and consistent contributors. But the biggest impact, and the one that makes this team a contender for potentially the next decade, is the leap that Jaylen Brown has made to flirting with all-star type of play, and Tatum getting thrown in to the fire and rising to the occasion.
If Gordon is here, Tatums development surely would have been stunted just simply by having far less minutes in the rotation. Does Brown get the confidence to take the shots he has been with a proven wing like Hayward on the court with him? Would that even be in the gameplan? My guess is no. Brown would be a 4th option at best in most offensive situations.
So we have to look at it this way. Even with Hayward, if we did make it past Cleveland to the finals, we would likey lose to Golden State, with not much of a series. But now that we have bonafide, tried, and proven 3rd and 4th offensive options in Brown/Tatum, we have a great chance at actually contending in a seven-game series with any team in the league.