Last season Aminu averaged 17 and 9 in the playoffs on 52% shooting (43% from three) and they still got swept by a 6-seed. Pelicans averaged 112 ppg in part because the Blazers had no one who could stop Jrue. You have to expect that The Brow is gonna get his against anyone, but if Jrue Holiday is averaging 27 and 7 on 57% shooting, you screwed.
And because of the other deficiencies the defense is completely dependent on Nurkic. Before he came they were terrible on that end, now they're up to above-average only if both him and Aminu are in the game, and they fall way the hell off when Nurkic is out. Lilliard and C.J. are both net negatives on defense, and you can't have that from your guard duo in a tough playoff series. When you watch C.J. it's crazy how no matter how good he is offensively, he gives away damn near all of it on the other end.
Regular season team defensive ratings and ability to get anywhere in the playoffs with it are not the same thing. Portland hasn't won a series this decade except for that one where all the Clippers' stars got hurt (and they were on their way to losing before that). Hell, outside of beating the Clippers with no CP3/Blake, McCullom has only won 3 playoff games in his entire five-year career. And the deficiency is not in their offense.