ultimately you could channel your hatred into a gamechanging event ^^
Get your characters into a trap, enemies don't always have to sit waiting above ground ! Cut one of his wings off ! ^^
Do whatever you want with him and see how he deals with it.
Just because the GM is a mean motherf**** doesn't mean it's not fun ^^
There are so many things you can do to a windling if you think about it. You could get your group involved with a globberog and the slime could hinder the windlings ability to fly for days. If you wander about in a cave or a desolate area, sometimes its better not to use your last bit of water to clean the windlings wings.
You could also stress the wild nature of the Zoak a little more. Animal insticts can always be played out to the player's advantage but also his disadvantage.
For example I have a windlings in my group that decided to befriend a Jub-Jub ^^
Even though it turned him into a little bit of a Squiq-Rider-ish thing (Warhammer) his new found companion also has his downsides.
Giving an animal certain traits can make things more interesting. The Jub-Jub for example has bad eyesight - almost once per fight it mistakes his little master for something to eat and lashes at him

PS:
I know alot of the things I suggest sound radical but it's only to inspire you a little into thinking out of the box.
A windlings above the treetops scouting cannot see what is going on below the roots, that is a fact. A zoak certainly has instincts that kick in when a situation gets too dire and unless the bond is magical I don't see how it would sacrifice it's own life for the sake of it's owner.
And since windlings have no versatility and Thiefs don't get animal bond there can only be a skill involved.