To frame this discussion, I’ll ask that you take a look back at the players who have won Finals MVP over the years. The vast majority of those players were either MVPs or widely considered one of the top 2-3 players in the game that year. For the most part, the outliers (for example Andre Iguodala, Tony Parker) were on teams that featured players who didn’t win Finals MVP but were clearly one of the premier players in the league (Steph Curry, Tim Duncan).
This isn’t to say that it is impossible for a team to win without a top-3 player in the league.