Pirandello's relativism, in the novel, does not say that everything is worth the same. It says that there is no ready-made reality, equal for everyone and for all time: each person gives shape to his own, the one he gives to others is true for whoever gives it, and a man builds himself the way a house is built.
The idea builds up step by step. For each person, his own consciousness is not enough, because there are the consciousnesses of others. The reality of the reader, of Moscarda, of the neighbor is a presumption that comes apart when another person sees it from outside. Words are empty, and each person fills them with his own meaning. The conclusion, on the return to the city, is that there is reality only in the momentary form we give to ourselves, to others and to things, and that the reality one person has for another is real for him, and not for the other.
Book III says that facts, forms and acts are prisons: whoever wants to be must bind himself to a form, and each form exacts the penalty of not being able to be anything else. And Book VII gives the other side: what others imagine of us is really possible, and is true for them. If we do not hold on to the reality we have given ourselves, others may convince us that theirs is truer. This is what happens to Moscarda with Anna Rosa.
The book, however, does not celebrate this. For the one who lives, no reality is truer than another, and all of them last an instant. Moscarda suffers, and the novel shows the price.