Many years ago I read a story
The Only Thing We Learn, a short story by Cyril M. Kornbluth, also the answer to this old question; first published in Startling Stories, July 1949, available at the Internet Archive (click here for download options).
about a university class
The professor, though he did not know the actor's phrase for it, was counting the house—peering through a spyhole in the door through which he would in a moment appear before the class. He was pleased with what he saw. Tier after tier of young people, ready with notebooks and styli, chattering tentatively, glancing at the door against which his nose was flattened, waiting for the pleasant interlude known as "Archaeo-Literature 203" to begin.
dealing w/ a saga about how an empire was overthrown.
"We shall examine first, by our archaeo-literary technique, the second book of the Chant of Remd. As the selected youth of the Empire, you know much about it, of course—much that is false, some that is true and a great deal that is irrelevant. You know that Book One hurls us into the middle of things, aboard ship with Algan and his great captain, Remd, on their way from the triumph over a Home Suns stronghold, the planet Telse. We watch Remd on his diversionary action that split the Ten Suns Fleet into two halves. But before we see the destruction of those halves by the Horde of Algan, we are told in Book Two of the battle for Telse."
[, , , ,]
"That much we know." The professor saw they were tiring of the terse scientist and shifted gears. "But if the veil of time were rent that shrouds the years between us and the Home Suns People, how much more would we learn? Would we despise the Home Suns People as our frontiersman ancestors did, or would we cry: 'This is our spiritual home—this world of rank and order, this world of formal verse and exquisitely patterned arts?"
Details of the saga were discussed such as how it said the defenders had empty bellies but archeological discoveries had shown that was false.
Not exactly, but you're probably remembering this passage:
"And so on. Now, as I warned you, Remd is of the Old Epic, and makes no pretense at fairness. The unorganized huddling of Telse's population was read as cowardice instead of poor A.R.P. The same is true of the Third Canto. Video-cores show on the site of the palace a hecatomb of dead in once-purple livery, but also shows impartially that digestion of their last meals had been well advanced. They didn't give such a bad accounting of themselves, either. I hesitate to guess, but perhaps they accounted for one of our ancestors apiece and were simply outnumbered. The study is not complete."
Mention is made of fighting on the edges of the currrent / successor empire,
The professors lecture was drawing to a close. There was time for only one more joke to send his students away happy. He was about to spring it when a messenger handed him two slips of paper. He raged inwardly at his ruined exit and poisonously read from them:
"I have been asked to make two announcements. One, a bulletin from General Sleg's force. He reports that the so-called Outland Insurrection is being brought under control and that there is no cause for alarm. Two, the gentlemen who are members of the S.O.T.C. will please report to the armory at 1375 hours—whatever that may mean—for blaster inspection. The class is dismissed."
Petulantly, he swept from the lectern and through the door.
and the professor comments "the barbarians always win."
That may be the moral of the story, but the professor in the story doesn't say anything like that.