We don't win a title with Kyrie as our best player
Not about this discussion. Just one point ... about the team in general. Not really Kyrie.
I do not see this team as it is built to be in the typical title winner build. Where you have best player (Jordan, LeBron, Shaq) and supporting stars (Pippen, Bosh, Pau Gasol). I see it more along the lines of the 1979 Seattle Supersonics or 2004 Detroit Pistons. A team that wins with multiple lower level stars (non MVP, outside top 10 stars) rather than one built around an MVP type talent.
On that 1979 Sonics team, you could argue any one of 3 players was their best player = Jack Sikma, Gus Williams or Dennis Johnson. Lots of quality depth around them as well in John Johnson, Lonnie Shelton, Freddie Brown and Paul Silas.
With the 2004 Pistons, one could argue any one of 4 players in Ben Wallace, Chauncey Billups, Rasheed Wallace or Rip Hamilton. Great depth around them as well (Tayshaun Prince, best bench in the league with Corliss Williamson, Okur, Campbell, Mike James, Lindsey Hunter).
I see 2018 Boston in the same way. Multiple stars in Horford, Kyrie, Hayward, Jaylen and Tatum. Great depth in Rozier, Morris, Smart and Co.
.... so back to initial point. Whether Kyrie or Hayward or Horford fits typical best player on a title winner, I don't really care about that. I don't think this team as configured has that type of player (MVP candidate) or needs to have that type of player (because it has 5 All-Star talents instead). It wins (or needs to find a way to win) with depth of star talent (5 guys) rather than true 1-2 marquee individuals.