The importance of the Last Dragonborn is that they are the only one who can kill a dragon permanently, but the alternative is never shown outside the initial resurrections.
Imagine if you could hear that while the dragonborn was studying with the Greybeards, a dragon attacked Solitude and was killed by the defenders.
Real heroic except for the part where Alduin swept back down 3 days later and brought the dragon back. Now a third of solitude was burned before they left.
The fourth era actually has more capability to slay dragons than the merethic era heroes did, but it still doesn't matter because Alduin will always win a war of attrition. It becomes a race of trying to break up skeletons and get the dragonborn to them.










