What happens if your mandamus application fails? Remember you have one lawyer and they have hundreds of them. You still have a citizenship app after becoming a pr.You need to hire a lawyer.
Delays can be caused by some vague issues in your case which require in-depth examinations. When you take someone to court, their lawyers will put your case under microscope and suddenly many more vague issues will arise which would require in depth examinations. The additional quantity of vague issues will only convince the court on the need for further examinations which again only delays your case and turns your life to a court battle. The real question is why cases are delayed and what is the objective? Is it because they are afraid of granting pr to a complicated application? Or to leave it up to the applicant to self deport themselves? Or to set an example to discourage similar applicants... or is it just lack of resources? Maybe the time spent on such applications could be used to process more simpler applications? Without knowing the underlying reason, simply filing a mandamus can have unintended consequences.