In reading The Aeneid again recently, in particular the end of Book IV where Dido kills herself with Aeneas' sword. Vergil doesn't use the word "gladius."...and as I thought about it, it was apparent he rarely uses the word gladius in the whole work.....
The Perseus site has a tool showing word frequencies among the common Latin works of lit.... https://www.perseus.tufts.edu/hopper/wordfreq?lookup=Ensis&lang=la
Vergil usually uses words like "ensis," "ferrum" (cf- our "steel") or "arms" (arms). More rare words like pugio (dagger), sica (knife as a murder weapon) or culter (cutting edge, as in our cultivate) occur only once or twice in every 10-20,000 words.
According to the Perseus tool, Vergil uses gladius only 9 times in the whole Aeneid. Livy uses it 96x in Ab Urbe Condita (Books 1-10) while Caesar uses it 24x in his Gallic Wars, a shorter work.
For the word ferrum-- Livy 169x....Vergil 174x....Caesar 43x
Arma-- Livy 750x ...Livy 554....Caesar 182
and Ensis-- Livy only once...Caesar not at all....and Vergil 63 times....so I guess we're justified in calling "ensis" a poetic word for sword.