messing up with the leathercraft, I did have general question about finishing edges as you, but not only for thin leathers (btw - 4/5 is not much thin) .
and you now what? - you're dam' right - it wears off and become ruined over the short period of time.
I did my best, tried several methods as you..
The only thing that looks good and stays much on the edge is the leather edge paints (not just dye, but flexible coat).