Macross Frontier, both the TV show and the films, rely on a lot of reading between the lines and implication to tell its themes and story. And the film edit is a bit more direct and on-the-nose about telling the same story and themes in general. For example, in the TV show, Alto never explicitly chooses between the two heroines to close off the love triangle the way he does in the film. There's some ambiguity left for the viewers to make up their own mind, or to imply the triangle and love rivalry could continue. But that's not really the intent of the TV show when you do a formal analysis and also listen to the writers themselves. In the TV show, Alto connects with Sheryl in a fundamental way that he never does with Ranka. They also sleep with each other. When Ranka and the Macross Quarter depart the Frontier fleet, he stays behind with Sheryl. And the clincher (if you believe the writers): during the final battle after Alto saves Ranka and delivers her back to the Macross Quarter, he then flies over to where Sheryl is on Battle Frontier, and salutes her directly in person before taking off to the final battle - in a very intentional callback to Hikaru Ichijo's iconic saluting of Misa in the final battle of DYRL.