You really miss the fact that Alto's name comes first in the cast, he is the main protagonist, the one taking this journey, and therefore should receive more screen time. He is a more interesting character than Sheryl given his background. She is frozen in one place and will never move. However, Alto had true potential to shine greater than ever before and they let that slip through their fingers. He was downplayed to a generally emo gender-bender who wants to fly and protect his home. None of that was his original character. But because Sheryl has to take up 90% of the movie, Alto is not important to them, never mind that he is her romantic interest.
But still, I am not delusional. I wanted to see more of Klan especially. She attracted my attention in the series for being the most daring female character in the show. Do not forget that she is also the one to make Michael shine. Her missing as a character that assisted greatly in the movies depressed me. She was downplayed to just being a random person who shows up and has connections to the main characters via the military.
Michael really had an interesting background with his sister's death and how he came to fall in love with Klan, even how he met Alto (drama CD); but they downplayed all of this to him being just an insight character with some support to the protagonists. However, his friendship with Alto then became questionable because they never gave any background information about whether they were friends or just comrades (at the base), since the story is altered from the original series version. Their interaction time to justify their exact relationship with one another is very little. The closest scene to friendship between them is almost at the movie's end, in which Michael tries to slap Alto and they have a bro moment. That's it. And I felt that Michael was truly an inspiration to Alto in the series but they felt that wasn't important at all, never mind that Alto grew with the help of Michael.
Shall I even approach poor Luca in this matter? He was one of the few characters we barely saw enough of in the series and knew very little, if anything, about him. Given that his sister is dating Mishima, that gives a very interesting plot but they all but slapped it aside. Take notice that we are left unaware if his sister ever survived the Vajra war. Also, his relationship with Nanase is torn apart completely. They never actually meet in the movies. I felt that it was Nanase who helped Luca mature into a man in the series and they slapped that aside completely.
Nanase was the worst of the side characters. She got a total of two scenes in the movie and only one line. Her friendship with Ranka that was so nice was gone completely. This downplayed her role and also severed her tie with Luca. They really screwed up there.
Ozma is one of the most badass male characters in anime. The series proves it. But his role in the movies is very little. He is used as a plot device to be lost with Sheryl, one whom in the series he didn't care for a lot, and doesn't get to even show his feelings for Catherine one bit besides the date. They avoided all of his character development to allowing Ranka to grow. Plus, there is very little interaction time between Ozma and Ranka, thus destroying the bond they had for new viewers.
I won't state any others but a good story builds from the secondary characters up to the main characters, working in their relationships with one another and how that secondary character can help improve on the main character. The movies did no justice to this at all.