How would you explain that in English the progressive and perfect are necessary when,?

Question

in fact, from a logical point of view, they are wholly arbitrary?

Answer 1

Nothing in language is ever necessary, of course, except to those who want to express the concepts that they entail. Other than such an answer, I have no idea what you mean. The progressive and the perfect tenses are only necessary when one wants to express ideas that are expressed using the progressive and perfect tenses.