... and would confuse audiences that didn't watch DS9.
Ah come on. Audiences are not stupid. There's a space battle, and then they drop a line how they are at war for 3 years with the Dominion. It's not that hard. And it's not confusing
How does that help the story?
Showing the battle and injuries and losses helps the story by showing the importance of a fountain of youth. Show, don't tell.