I always just come back to history on this one.
The last time a team won the championship without a top 5 player, was the 2014 Spurs and they had 4 HOFers and the core had won multiple championships.
Before the Spurs, it was the 2004 Pistons. Before that you are back in the 70's with the Sonics and arguably the Bullets (Hayes was close if he wasn't one).
Historically you just don't win a championship unless you are anchored by a top 5 player. Tatum is a not a top 5 player, so it shouldn't be a surprise Boston hasn't won the title.
Don’t forget the Mavericks…
Dirk was a top 5 player that year.
Nope. His MVP season was back in 2007. Mavs won in 2011. He wasn’t at that level anymore. Still elite; but not top 5. Derrick Rose won MVP that year, Dwight was runner up and then you still had Kobe, Lebron, KD, and Wade.
And Dirk outplayed all those guys on his way to the title. He outplayed Kobe in the 2nd round to beat LAL. He outplayed Durant in the Conference Finals to get to the Finals. And then Dirk outplayed both LeBron and Wade in the Finals to win the title.
Even though Nowitzki outplayed these fellow stars in a series doesn't automatically make him a better player. For instance Tatum has outplayed Embiid in a series, but few people would argue that Tatum is on the same level. Butler has had multiple dominant playoff-runs and still he's never in the discussion for MVP. Sometimes it's also about match-ups. Leonard always was a burden to LeBron James. There's no argument that he was ever on par with prime LeBron.
No, I think Moranis has to give in here. I would argue that Curry last year also wasn't necessarily a top 5 player anymore (8th in MVP-voting for instance). Top 5 is of course an arbitrary number. Broaden that to a category of legit MVP-candidates (type A) and franchise players (still All NBA-level) with a lot of playoff-experience (type B) and it makes the underlying argument for Moranis stronger.
We can classify Jokic and Embiid as type A. In my opinion Doncic is also a type A, but the Dallas roster is pretty bad. And you have Antetokounmpo who's probably still a type A, but certainly factors as a type B.
Besides them, the current NBA-situation is very interesting because there are a lot of older legends who deserve the status of franchise player. Although there are question marks about decline, health and supporting casts I would add this list as type B candidates (Curry, Durant, Butler, Leonard, Lillard, Davis, James, Harden). I scratch Harden and James. But can Leonard or Davis ever stay healthy? What team will Lillard be on? It's a tough group to judge.
On the other side you have a new generation which is still in a team building process and not quite MVP-caliber (SGA, Morant, Williamson, Haliburton), but under the radar SGA is close. The generally often overlooked middle group is quite small: Tatum, Booker, Mitchell, Sabonis, Young, Towns. With the emphasis on the combination of quality of a franchise player (or All NBA) and playoff experience I'd have to dismiss Sabonis, Young and Towns.
And that leaves Tatum, Booker and Mitchell as to be added as type B guys. The term franchise player is perhaps too vague here, so clear All NBA-level as a judgment will suffice and all three have lots of impressive individual playoff performances in their bag and they have strong supporting casts. Both in support and consistency Mitchell is on the edge.
In the strict sense of Moranis' claim that you need a definite top 5 player to win (and obviously some decent help) it would make the Nuggets the title favorite again with the Bucks and the 76ers as only legit contenders. That's a pretty bold statement. By using my criteria you can add teams like the Suns and Celtics without having to do some retrospective discussion on Tatum, Booker or Durant in case they win the title.
My overviewFavorite: Denver Nuggets (Jokic-A)
Contenders: Phoenix Suns (Booker-B, Durant-B), Boston Celtics (Tatum-B), Milwaukee Bucks (Antetokounmpo-A), Philadelphia 76ers (Embiid-A)
Outsiders: Miami Heat (Butler-B), Golden State Warriors (Curry-B), LA Clippers (Leonard-B), LA Lakers (Davis-B), Cleveland Cavaliers (Mitchell-B)
Note: Portland, Dallas and Oklahoma City are excluded, because it's unlikely for Lillard to stay and these teams probably lack the supporting casts to compete, but Doncic (A), Gilgeous-Alexander (potentially A) and Lillard (B) in a different setting theoretically could lead a team. As I said I excluded James and Harden from that guaranteed All NBA level and therefore not classified as a type B, thus not a potential best player on a championship team.