The other quality that Brown brought to the finals this year, along with his D and his offensive bursts, was intangible but, IMO, vital. It was an emotional component -- a vibe. It was predatory and ruthless and alpha angry and it infused the team with an edge they sometimes needed.
The other leaders of this team -- think Tatum, Jrue, D-White, Al -- are incredibly poised, even-keeled, somewhat softspoken, almost to a fault. The team was remarkably resilient and confident and goal-focused because of those qualities.
But every once in awhile the C's needed a degree of anger, a flair, a thunder-dunking display of dominance. More often than not during the season it was Jaylen that provided that element. Definitely during both the ECF and the Finals it was Jaylen who flexed, who cussed, who voiced some of the pent-up frustration, who in-your-faced everybody standing in the Celtics' way. All of that nature-film Orca ruthlessness CJM was trying to infuse the team with? I think it was often Jaylen who projected that threat of being not just skilled, but dangerous -- and who (I'm speculating here, I admit) may have spread it through his teammates.
All of this unquantifiable. It might reflect (and fuel) a fan's perception as much as represent a strategic internal reality for the team. But I am convinced it lent a certain charge to this version of the Celtics -- a charge that may well have been a vital ingredient in this year's championship.