There is nothing false about that. Talent is what wins and it always has. The Warriors first title run their 3 best players were 26, 24, and 24. They had another starter that was 22. They of course had some veterans, none of which had title experience, but every team has veterans. The Thunder basically made the Finals with the entire roster on rookie contracts (just about anyway). Lebron made his first finals appearance at 22.
You skip over the fact that the Thunder made the Finals when they were young ... and got smoked.
LeBron made the Finals at age 22 ... and got swept.
Talent is a necessary ingredient for winning, but it's also very hard to win playoff series when your team is very inexperienced! The teams that win the title are almost invariably stocked with veteran players, whether it's the main guys or the players around them.
The Warriors, as you concede, may have had a young core, but they also had key veteran role players. Iguodala, Livingston, Bogut, David Lee, Barbosa, Mo Speights ... these guys had been in the league for a long time and collectively seen a lot of playoff games.
Then of course you have their coach who won titles with multiple teams as a player.
That's what we're saying here ... the Celtics need more talent on the roster, yes. But also, particularly because their leading scorers are so young, they need an experienced, veteran, disciplined supporting cast.