Except, this is not a criticism. This is an attack. 

A brotherly criticism, would have been in private, preferably, in person and entertaining the idea that the Post Synodal Exhortation is actually right, and expressing the valid concerns it wants to address. Instead, what is given in a public letter, given to the media, in the form of a summation of the combined written reports of judge, jury and executioner. 

In short, this is neither brotherly, nor it is a criticism, but a shrewdly formulated merciless (personal) attack. As such, it is not honest. That is what the Pope is pointing out.