Using season summary information from Basketball Reference.com, we can glean some interesting information. Dating back to and including the 1977-1978 year, essentially the time of the ABA-NBA merger, there have been 35 Finals. While no definitive patterns emerge, there are numerous factoids that unfortunately tend to throw cold water on this year's banner quest.
Taking a look at the ultimate championship winner in each year, I used two methods. Let's call the first the simple method: offense equals the team rank of average points scored and defense the team rank of average points allowed.
Does defense win championships? By the simple method the answer is that it is not a guarantee, but it does improve your chances. 21 times (60%) the champion had a better defense ranking than offense ranking. 13 times (37.1%) the champion was ranked top 10 in defense without being top 10 in offense. On the flip side, only 10 times (29%) was the winner ranked top 10 in offense without being top 10 in defense (curiously, 7 of those 10 were the Lakers). Never has the winner not been ranked top 10 in at least one or the other. 12 times (34.3%) the winner was top 10 in both. Only twice did the winner rank in the bottom third in one or the other.
The second method I looked at was similar, but this time used ORtg and DRtg. For those not familiar, it is an estimate of points scored or allowed per 100 possessions. The idea is to adjust for pace. This method changes the results perhaps not dramatically, yet with some significance.
Returning to the question, Does defense win championships? what we find is that 18 times (51%) the winner had a better DRtg than their ORtg. Only 6 times (17.1%) did the winner have a top 10 DRtg without also having a top 10 ORtg. On the other side of the coin, only twice did the winner rank top 10 in ORtg without also being ranked top 10 in DRtg. 28 times (80%) the winner was ranked top 10 in both categories. And the most ominous sign, only once (2.9%) did the winner rank in the bottom third in either category (2000 Lakers - 2 ORtg & 21 DRtg).
And the answer is? The second method is generally preferred by analysts over the simple method. It shows that while defense is an important if not essential component of a championship team, by itself it is rarely enough (17.1% chance). A champion still needs decent firepower on the other end. One could make the argument that defense is more important than offense, but not so much so that offense can be totally overlooked.
So where is the cold water? With only four games left, it is unlikely that the various rankings will change much. Including last night's game, the Celtics by the simple method rank 19th in points scored and 10th in points allowed. By the second method, the rankings are 24th ORtg and 6th DRtg. I would not call myself a fanatical fan, but I do love my Celtics and nothing would make me happier than to see them beat the odds. Realistically though, it is a real long shot as they just don't score enough points to go along with the upper echelon defense.
Not a consolation, just an observation. Of the 17 playoff teams (I say 17 since the 8th spot in the West is still not settled) Milwaukee (21st in ORtg), Chicago (23rd in ORtg), and Utah (21st in DRtg) are long shots too. Conversely, 4 teams fall in the 80% category where they are top 10 in both ORtg and DRtg - the Heat, Thunder, Spurs, and Clippers. Still, it's the playoffs. Anything can happen!