Manhattan was "planned" inasmuch as the grid system was created, but the exact character of each neighborhood wasn't laid down in advance. Defining "planned" is a matter of drawing a line on a spectrum, so there's a lot of arguments possible here.

What I mean is to compare Manhattan, which was loosely planned, with Levittown (https://en.wikipedia.org/wiki/Levittown), rigidly planned, which was the original planned city and the grandfather of overly aggressive city planning. Later this evolved into the dystopian monstrosities envisioned by urban megalomaniacs like Le Corbusier such as Ville Radieuse (https://en.wikipedia.org/wiki/Ville_Radieuse) which would have been so utterly unliveable.

He honestly should have stuck to architecting open-air prisons and slaughterhouses.

Even Manhattan got bludgeoned by overly aggressive planning in the 1950s and 1960s when tyrants like Robert Moses were involved.

Creating great urban spaces takes a lot of patience, care, and most of all, a willingness to let the city grow as it wants to, not as you intend it to.