Six foot tall Kemba is a defensive liability but six foot tall Chris Paul and six foot tall Kyle Lowry aren't.But they are great defenders (or at least very good at this point still). It isn't so much Kemba's size, it is the fact that he isn't a good defender and being small with a smaller wing span doesn't help. If you are 6'6" with a huge wing span, you can be a lesser defender and still be able to have an impact defensively, but you just don't have that when you are small and a bad defender. And Kemba is a bad defender. He isn't Irving and he isn't IT4, but he still is bad.
That logic makes zero sense to me.
But is Kemba really a bad defender?
Yes, he can be pushed around and shot over when posted up close to the hoop. But that is true of almost all small guards. That doesn't make a player a bad defender. It more often means he's in a system that doesn't prevent that mismatch.
On perimeter shot contention, Kemba is among our better players - his opponent 3PT% differential of -7.3% is fantastic, and 3rd best on our team behind just Smart and Tatum.
And Kemba is one of the best in the league at staying / getting in front of players and drawing charges. He averages drawing a charge about once every 3rd game -- way more than even Marcus Smart (about 1 every 5 games). And that has been true about Kemba for the prior couple of seasons as well. These are real and significant defensive 'positives' that Kemba brings to the floor.
So far this year, the Celtics have had a Defensive Rating that is -1.6 points better without Kemba on the floor. But since mid-January, the difference has been just -0.7. That's hardly compelling evidence that he is any sort of big defensive albatross for us. In fact, since Feb 1, the team has been -4.9 points per 100 better
defensively with Kemba on the floor than without.
Last year, with Kemba in the starting lineup and consuming large minutes with this team, the Celtics were still the #4 defense.
Maybe he's not a great defender, and he's certainly a small
defender, but I don't think it's quite correct to say he is a bad defender.