So, I suppose this is one of those episodes where everyone with speculations can say they were correct in a way.
It became pretty clear at the beginning (as soon as she started the fake-crying) that this was all an act she was putting on after all -- a front thick enough to keep even Junichi out, but designed around a preconception that this was who he wanted her to be. So indeed, he just needed to affirm that he liked
all sides of her (including that inner part) and she could be herself with him again. It was due to that inner, honest part that he fell in love with her, so without that she just wasn't the same. The funny thing is that, in a way, this means that Junichi's idea was actually right -- that apologizing and getting everyone's help would make the festival work; that's just what she did and all was well with the festival. And it did come out after all that -- deep down -- she had an objective beyond just her pride and selfishness in making the festival a success as well (it wasn't
just about looking good on her resume -- her kindness isn't
all part of the facade), so he was right to assume that making the festival work was important to her (and more important than her pride). And in the end, he was able embrace her honestly and completely, and showed that he understood that both sides of Tsukasa were good and he wanted it all. That along with the revelation brought things into balance, and now Tsukasa can be her "true self" with him (warts and all), demonstrated by her opening up and telling him about her past, and the change from an "agreement" to a "promise".
So in the end, it's a "perfect ending", but still a bit less than "pure"; it sort of validates that you might need to use a facade with others to get ahead, but you should at least be honest with those you love. Perhaps that itself is just being honest, too.
And the epilogue was great, of course. Hope the Blu-Rays add one for the other heroines that were missing one.