Three of the seven best defensive lineups the Celtics deployed last year, by the numbers, featured Jameer Nelson and Kelly Olynyk:
http://stats.nba.com/league/lineups/#!/advanced/?Season=2014-15&SeasonType=Regular%20Season&TeamID=1610612738&sort=DEF_RATING&dir=1
Rajon Rondo graded out as a better defender than KO last season. So did Gerald Wallace:
http://www.basketball-reference.com/teams/BOS/2015.html?lid=header_teams
Jared Sullinger averaged more blocks than Olynyk did. Olynyk's one steal per game is good, but considering Al Jefferson is close to that, and I think you'd agree that Jefferson is hardly a good defender (and my suspicion is that you don't think Sully is a particularly good defender either).
I would maintain that most everyone on the Celtics had their defensive numbers inflated by their system -- the system that allowed them to finish 12th in the league in Defensive RTG overall, and this particularly applies to Kelly Olynyk, who also did not post his numbers playing starters minutes, and is unlikely to maintain them if he ever cracks 30 minutes per night -- something to take into account when you're casually extrapolating per-minute stats.
That is one reason, probably, why Olynyk's defensive numbers are inflated towards something you could squint at and say "they're good", especially if you wanted to see him stay with the Celtics -- a notion you've expressed on multiple occasions.
I'm trying very hard not to be casual about interpreting the stats. I admit that I'm a big Olynyk fan and that I'm biased towards him. I want to see him do well, and I appreciate any evidence that suggests he's doing well.
Given the above, I take heart in the numbers that show almost unanimously that he's a plus defender. I've looked at more or less every stat available to me (not the ones you have to pay for), and they say he's a good defender.
Despite the numerical evidence, though, almost everyone around here claims--often forcefully and derisively--that Kelly's a lousy defender. I read a lot of phrases about him being "soft" or "lacking aggression" or being "weak" without any real analysis of his actual defense.
I've considered the "over-inflated" stats argument. It's reasonable to surmise that his stats look good because the team's overall defense is good. However, when you look at his on court/off court stats for last season, they show that the team was considerably better defensively when he was on the court than when he was off the court.
I understand that this naturally leads to your next argument; that Kelly's defensive stats are inflated because he played primarily against opposing bench players. If this were the case, though, I would think it would be a general rule that bench players across the league would post better defensive stats than their starting counterparts. Kelly's not the only bench player in the league who played primarily against opposing bench players, right? In looking at defensive stats for players across the league, though, this doesn't appear to be the case at all. there are tons of non-starters with lousy defensive numbers.
Now, don't misunderstand me here; like most of you, the eye test does not tell me that Kelly Olynyk is a great defender. I've seen him make a lot of mistakes. I've seen him get overpowered by bigger players and I've seen him get burned by faster players.
However, I've also seen things defensively that impress me about Kelly. He often shows good awareness in the lane on pick and roll plays. When he drops back to cover with a ball handler charging and a big rolling, he's generally good at not over committing to either too early, doing his best to disrupt an easy finish. He has quick hands (although not much length) which often allow him to make plays on the ball in these situations.
As a post defender, he can get overpowered, as I said earlier, but he generally at least fights for position to try to make an easy score more difficult.
I feel that his biggest weakness defensively is on the perimeter. He really can't guard quicker fours, never mind being able to switch onto threes. These situations are a nightmare for Kelly. This is where it seemed to me that coach Stevens did a very good job protecting Kelly. He didn't put him in a lot of situations I can recall where he was forced to guard quicker perimeter players.
Despite his "soft" label, I think his best role moving forward is as a center. If he can be paired with a long, athletic, shot blocker at the four like, say, an Amir Johnson, Kelly can guard the lane in the pick and roll, be asked to bang a bit with opposing centers, and be bailed out by his PF partner with weak side shot blocking help.
He can hold his own more defensively at center than at power forward, and he can create more of a matchup advantage for himself, and the team as a whole, on the other end of the floor with his perimeter oriented offensive game at the five position.
I don't expect to change the general perception of Kelly Olynyk as a soft player who can't defend. I don't expect people to not continue to see what they are already predisposed to see.
I do, however, ask that perhaps, when using the "eye test" this upcoming season, that folks take the time to not only look for the things that Olynyk does poorly defensively that confirm these preconceived notions, but also to keep an eye out for the things he does well defensively.
