On the one hand, it was built patiently with its core stars running together for a long time, each year they progressed and improved slowly, until (possibly?) the moment they are good enough to be a champion. Also, none of its stars signed there in free agency, it was built through draft and trades. Also, it doesn't have players who are viewed top 3 in the league, only one that is top 5/top 10.
On the other hand, it is a team that has 5 players of All-Star caliber - 4 of them were All Star already at certain points, plus a sixth guy who is a former All Star. For me, when the team's skeleton was formed in the offseason with Holiday and Porzingis, it had a superteam vibe.
Wikipedia describes the term "Super-Team" as follows:
A superteam in the National Basketball Association (NBA) is a team that is viewed as significantly more talented than the rest of the teams in the league. There is no official distinction, but it is generally viewed as a team that has at least 3 Hall of Fame, All-Star, and/or All-NBA caliber players that join forces to pursue an NBA championship.
Boston pretty much fits the description, but it depends on the meaning you attribute to the "join forces" part - because the players themselves didn't decide to join forces like in other historical cases, but were "put together" by a GM (it can still mean that they "joined forces" at the end).
So, which side are you on this?