The difference between has been and was that it has been being used in the present perfect continuous tense, whereas was is used in the past continuous tense. It has been means it has been continuous, or you could say it has to do with something that was but is no longer. For the former, you could say “Susan has been quiet all night.” For the latter, you could say, “Madonna is such a has-been.
Her songs are not like they used to be.” Was is used to refer to the past, but it is definitive. The form is used to refer to some action that was going on sometime in the past. The time or action may or may not be indicated, and an example is “She was brushing her hair 100 strokes every night”. It already happened sometime in the past.