They couldn't sign Hartenstein, that was part of the problem. Their offer couldn't exceed ~$12mm for year one with limited escalations. This is among the senseless things about the current CBA.
I believe the idea was to have KAT play the four (as Randall's replacement). Robinson missing most of the season injured screwed this up.
This is why it's time to move on from Thibs.
With a starting lineup of Robinson, KAT, Anunoby, Bridges & Brunson; with Hart as sixth man, the Knicks cam matchup well defensively at most spots. No other team has two wing defenders the quality OA & MB. With OG playing the four he was giving up too much height too often.
The Bridges trade didn't work out close to what was expected (the prior Nova additions all moved in seamlessly) and yes, KAT will always be deficient on defense. A trade for a competent starting center (presumably for Bridges & Robinson) would help quite a bit. A couple depth pieces will also be needed.