One idea I had is that these Power Rangers aren't the first, and there's been several teams beforehand.
After they lose a battle, Jason loses his confidence as a leader and runs off. He's then met a by a man that tells him about the importance of leadership and reveals he's actually the leader of the previous team, the Power Rangers Avian Fleet.
You're probably right. The only way Power Rangers will work as a movie is playing on nostalgia to some extent. That is why I would use the original MMPR zords if I was in charge, I mean they still make the toys for them so they are recognisable to kids and adults who grew up watching the show. I understand why they're trying to do something different but I think they'll just end up missing the point. The costumes will be horrendous I reckon.