The retired judge, Sir Martin Moore-Bick, specialised in commercial law (in particular, shipping). Whether that is more appropriate than a judge who had formerly specialised in other areas of law, such as health and safety, building and construction, etc. I really don't know.
He acknowledged that the scope of the inquiry was very narrow and, as such, was unlikely to seem adequate for those whose lives have been turned upside down by the fire. I think many of the people affected by this tragedy have confirmed that that is indeed how they feel, and many other people feel similarly.
I'm not sure it's correct to say that he is not the right person for the inquiry because he made a controversial judgment in the Westminster case. It is, I think, a judge's job to interpret the law as it applies to a variety of situations. Such interpretations can differ from judge to judge; that is why there is a system of appeal. I'm not sure it would be possible to find a judge who had always arrived at judgments that everybody agreed with and which were never overturned by a higher Court.
However, I think it is the case that one of the primary principles in law is that justice be seen to be done. Some people will think it is perfectly acceptable for this man to be appointed but it appears that many of the victims of this fire feel differently. On top of the unease felt about the previous Westminster judgment (whether that unease is justified or not), they see a white man from a privileged background - perhaps similar in many ways to the senior council officers who, it appears, ignored concerns about safety in the tower block - being appointed to head this inquiry.
I don't know what the answer is because I don't know if there are other more suitable candidates for the task. But if the victims of this fire don't have confidence in this man and have suspicions about his neutrality, then I can't see how the inquiry can be considered to have legitimacy.
Also, if this inquiry is only to look at the immediate causes of the fire rather than the sequence of events that led up to it - and who authorised certain decisions re internal and external building issues - then is it just down to the police to investigate these issues? Presumably, they would need a considerable number of experts to assist them. Maybe I haven't followed this all properly, but has May made a statement as to exactly how the many other wider issues (whether building regs are adequate, etc.) are to be investigated?