Two things that are slightly conflicting.
#1 - Is there a position more overrated in this league than point guard? You clearly don't need an elite point guard to win a championship. In fact, I just went back year-by-year to see if there was a single team that won a title due to having an "Elite Distributor". SHocking... none of them do. I had to go back to 1990 to find a single champion who had a PG averaging over 8 assists... and not surprisingly that was Isiah Thomas (who also happened to be the Pistons leading scorer):
2012 - Mario Chalmers - 11 points, 4 assists
2011 - Washed up 37 year old Jason Kidd - 9 points 7 assists
2010 - Derek Fisher - 10 points, 2.5 assists
2009 - Derek Fisher - 10 points, 2.8 assists
2008 - 4th wheel 22 year old rondo - 11 points, 7 assists
2007 - Parker - 20 points, 5.5 assists
2006 - J-Will - 9 points, 4 assists
2005 - Parker - 17 points, 4 assists
2004 - Billups - 16 points, 6 assists
2003 - Parker - 15 points, 3.5 assists
2002 - Fisher - 10 points, 3 assists
2001 - Fisher - 13 points, 3 assists
2000 - Ron Harper, I guess - 8 points 3 assists
1999 - Avery Johnson - 12 points, 7.4 assists
1998 - Ron Harper 6 points 2 assists
1997 - Ron Harper - 7 points, 3 assists
1996 - Ron Harper - 7 points, 3 assists
1995 - Kenny Smith - 10 points 4 assists
1994 - Kenny Smith - 10 points, 4 assists
1993 - BJ Armstrong - 11 points 3 assists
1992 - John Paxson - 8 points, 3 assists
1991 - John Paxson - 8 points, 3 assists
1990 - Isiah Thomas - 20.5 points, 8 assists
... So traditional point guards don't mean crap in this league. What's also not surprising about that list is that essentially EVERY SINGLE TEAM had an elite scorer and an elite big man... or in some instances just an elite big man. Whether it's Dirk + Tyson Chandler... or KG + Pierce... or Shaq + Kobe. Or Hakeem + Drexler. Wade + Shaq. Duncan + Parker/Ginoboli. Kobe + Pau. Even last year, you have to count Bosh as an elite Big to go with LeBron. That is, if you aren't just counting LeBron... who is 6'9 and 270... qualifies as a big most decades.
You want to talk about that flukey Pistons team? Fine... they had two elite bigs (Wallace Brothers)... don't forget that Ben Wallace averaged 14 boards, 2.3 blocks and 2 steals in the playoffs. Rip Hamilton averaged 22 points in the playoffs... Billups was important, but bigs and scoring win titles.
Even the freakin Chicago Bulls... yes, they had two of the greatest players of all time (Jordan and Pippen), but they won their first 3 with all-star big man Horace Grant... and they won their next 3 with Dennis Rodman. Certainly not a traditional "big man", but Rodman was a two time defensive player of the year at the PF position and the best rebounder in the league. What more do you need to qualify as an "elite big".
#2 - Conflicting with above is the fact that the league is evolving into a small-man's game. Scoring point guards are all over the place. You may in fact have a team win a title with a Derrick Rose leading the way... or a Russell Westbrook as a key scorer. Clearly this year TOny Parker is a driving force for the Spurs offense (averaging 21 points). Chris Paul is a mighty distributor, but he's also his team's 1st or 2nd option on offense. Kyrie Irving is the hottest young star in the league (dropping 24 a night). If you cant go out and get one of those dynamic scoring point guards, it seems a solid defensive point guard would be nice to have in your arsenal. I like Bradley as our starting PG. Sure, we probably aren't winning a title unless he's our 5th best starter, but I'm comfortable focusing on the other positions. Trade Rondo when the package is right.
Side note: I'm sure Ainge realizes this. Part of the reason he's been trying to trade Rondo every single year.