Keep in mind that plot and story are fairly different things. The ST definitely has a story (i.e. stuff happens), however the plot (i.e. “a series of events deliberately arranged so as to reveal their dramatic, thematic, and emotional significance”), that’s an entirely different argument. Plot-wise the OT and PT are very complimentary stories, where the same themes are played out in reverse, Anakin is seduced by evil, Luke deafeats the darkness it and becomes good, etc. etc. The ST is very much a copy of the OT in both story and plot, with the quality of both being highly debatable.
An interesting question would be; what could the ST have done to compliment the PT & OT? Though this is hardly the thread for this discussion.