Rouliawkward realization that blender animation interpolation is set on each key, while in godot it's only on each track. Weirdly some of my imported tracks have constant interpolation, other linear, and I don't really know what does Godot take into account to make this decision.
So I'm guessing my best bet is to go "full linear" and duplicate keys to achieve a constant effect (put the duplicated key the frame before the next pose key). But not only does it add many unnecessary keys, I also wouldn't work without switching the animation framerate to whatever I'm targeting in Godot (60). But I like to animate at 24fps... 💔