The plaintiff's argument is correct. If a defendant is an expert or professional, with special expertise, then legal questions relying on the notion of a 'reasonable person' take account of this by assuming the 'reasonable person' has the same training, expertise, skills and knowledge as the defendant. The question thus becomes 'was harm due to removing the wall foreseeable to a reasonable engineer specialising in reconstructions?'
State and territory legislation requires that the conduct of a person practising a profession should be judged according to the views current within their profession. Section 5O Civil Liability Act 2002 (NSW) is illustrative. It says that a person practising a profession is not negligent if they acted in a manner that (at the time the service was provided) was widely accepted in Australia by peer professional opinion as competent professional practice. However, the court can disregard peer professional opinion that the court thinks is irrational. Also, if the case concerns careless advice given (rather than some other action or inaction causing harm) the question of negligence will be decided by the court rather than by reference to the views of the profession.