By spreading to the Caeliar the values of diversity, of sharing knowledge, of equality, of mutual partnership -- by spreading to the Caeliar Federation values -- Hernandez saved the Caeliar from extinction.
This was not a story about Picard saving the universe; it was a story about the ideals of the Federation saving the universe. A ton of characters were caught up in it, and were affected by it, but this was ultimately a story about the value of morals more than characters.
Hernandez was the hero, if you want one.
I admit it was an unexpected creative choice to remove the agency of most of the main characters in the conclusion, one that at first did put me off a bit, but I don't think that lessens the force of the message or the heroism of the characters, as many get chances to show that heroism in other circumstances throughout the trilogy.