[maybe spoiler alert]
Yeah, Leo still had chance to recover tho from his depression, but he might will never be with Chase again. Still sad but... well this game don't want you to be happy - Echo curse.
For Flynn's route, i think it's the real route, because if Flynn didn't became the monster, then they will never saw any monster in the first place, but the possesion still likely be there - again, Echo curse, that what i called it. If Flynn still had control to his emotion, he would likely be a good monster, but seeing what happened and where the monster appear, i think Flynn still cared to them but he did wrong things, instead of helping them it make more mistakes. Like how he appeared when Jenna's parent is arguing.
I'm sad, but i think there is no way to escape the curse in this game and the prequel, i hope the sequel will have good ending or i might cry lol (jk). If it's not then it will be complete loop, until nobody lives there again (which mean, dead, or if they hop into the train [maybe it was the only way to escape from Echo])
Anyway thanks for discussing this, now i understand more than before.