The new with-expressions are a concession to the existence of initializers, which are themselves literally "stuff that should have been in the constructor" and are incompatible with immutability (hence the new init property hack).

The correct path would have been to require primary constructors for records as the only point of entry for data, declare initializers incompatible with primary constructors, and then just synthesize a method for creating copies - but hey, then you might as well just use Scala.