What does "usually" mean? I guess to some it might mean more than 50% of the time.
In the last 20 years, the Naismith winner has played on the NC winner 11 times ( and in the 31 years of the award, it's just 14 times). That's a significant contribution for the last 20 years, but that still leaves 9 teams that didn't get the NC without the best player, and why Baylor in 2013 was left off your list, I'm not sure. Many would consider Griner a transcendent player by her stats.
Simply put, having the top player with either a very strong cast or another top-5 player can often get you an NC, but there are times like with Griner and Sims last year, or perhaps a Naismith winner Catchings in 2000 backed by Lawson and Clement that still falls well short. On the other hand, move Beard and the Duke team from 2004 to 2005 and they could well have won that NC game against MD in a diminished year. There is no magic formula for an NC other than true grit to the very end.
I did say it doesn't guarantee it. I only glanced at the lists (hence the Baylor omission). You could change the word 'usually' if you like.
I would argue that WCBB is so different from the past; you can throw out the old statistics. They are as meaningless as 1872 baseball stats (hyp). Where can you draw the line? I have no idea, but just in watching Geno's teams over the years, it is no longer the same game as it once was (as Lobo has mentioned several times). It makes sense to favor more recent history in that case. Which is why I looked at (arbitrarily) the 00's.
Using just the Naismith:
Past 5 years - 4x (80%)
Past 10 - 6x (60%)
Past 15 - 9x (60%)
Past 20 - 11x (55%)
Those are big numbers imo. Obviously, this is dependent on what voters say (which is subjective too) in this specific analysis. The person voted the best, isn't always the best. For instance, Parker was a better player than Harding, I don't care about their stats that year. If I'm making a team of college players, I'm taking Parker over Harding. Since 1998, that's the only one of the Naismith's I'd have a big issue with though.
This year, I expect voters to vote for Odyssey Simms. Even though the best player might play for UCONN. So the percentage would drop.
At any rate, in WCBB, I'd consider having the best player one the most significant factors in winning a championship. It doesn't guarantee anything, as we've seen, but the odds certainly favor it.