I don't mind Mikasa and Eren being lovers (in fact I do personally ship them together although its not a huge ship for me). I don't even mind Mikasa losing it at times because of her fear of losing Eren that's very much a part of their relationship. Mikasa though isn't weak, her abilities being so much better then average is also a huge part of her story. That isn't to say the Eren couldn't save Mikasa sometime (since of course he does save her when they are kids theme wise it could work it told right) but it has to be told correctly in order for that to happen.
In fact it can be argued the Mikasa and Eren and Eren are gender swapped versions of the Knight and Princess trope. The only main difference of course is that Mikasa didn't fall in love with Eren simply because of his beauty, but instead because he taught her how to live in this world, and gives her something to live for.
Levi not being there just doesn't make any sense though. I'm not sure why you wouldn't include him in the story. It's true he isn't the protagonist, but he is a huge part of the lore.
Still I'd be interested in watching a dub or sub of the movie one day. In order to judge it on my own.