I really do not understand the widespread belief that Luna and Harry understands each others. Because they do not.
Yes, both of them knows how it can feel to be an outcast, Luna more so than Harry, as well how it feels to lose people you love. But that does not magically grant them understanding of each others as persons. They have shared similar experiences and that really is the end of it.
For an example, if I and a random person both have been involved in a horrible car accident at some point in our lives, we both know how it feels and the struggle to move on from it. But I still would not randomly understand anything else about that person, nor would he or she about me.
The point that really makes this so odd for me is that Luna is that one extremely obvious character that we know that Harry does not understand. He literally does not understand or follows Luna's view of the world or on life. He has no grasp about her interests or reasoning. He does not know how she thinks and why she does as she does. Harry has LITERALLY said this him self in the books. He consider her to be a good friend yes, but he is so painfully clear in his feelings of finder her to be odd and weird.
That does not have to be a bad thing to their friendship, as we see that it isn't, but it is a false claim ignoring everything Harry has said or felt about Luna when someone says that Harry and Luna understands each others. They understand certain experiences that both of them has gone through, and that is really everything.
On other notes, I could never see Luna with Neville either. I love Luna, but I love her for whom she is and not for something I wish her to be. As such it is painfully clear that she in the end would have to end up with someone like Rolf Scamander to be truly happy and have a true common ground to build their relationship on.
I support canon because I have actually read the books and seen what they feel and whom they love.