Cardinal Muller: "When a letter arrives, we always ask the bishop that he might take pastoral care of the victim, clarifying to him or her that the Congregation will do all that is possible to give justice.”
Prescinding from the question of whether that is the appropriate response, the question remains: Why not a simple acknowledgement that the complaint has been received?  It is a basic courtesy to acknowledge the letter, express pastoral concern for the writer, and explain the next step in the process.
There are complaints that Pope Francis has not moved decisively enough in establishing a procedure to adjudicate complaints about bishops. Perhaps even more important, he has not moved decisively enough against officials in the Curia and elsewhere who resist the work of reform. Why is Gerhard Muller still Prefect of the CDF?
If Cardinal O'Malley wants to retain (regain?) credibility, he will have to insist on the resignation or removal of obstinate hierarchs; or he must resign himself.