Arvo and Mikko will have a good ending? Like, together? :(
Well, the author was willing to put in not one, not two, but three intermediate Mikko endings into the game by this point. So it's safe to say there very well might be a universally good ending for them in the final game in a couple of years - Dawn Chorus receives monthly updates for one or two characters at a time, usually moving the plot a day forward for them.
In the meantime, you can read through the comments here for guidance on getting the bad, and the worst intermediate Mikko endings, just to not feel as bad about the ending you've got.
Also, other characters are very well worth your attention as well. But do be warned - the Torulf route is pretty heavy, while the Lake route is absolutely the lightest one. I really recommend playing the Lake route last just to walk away from the game with a positive impression.