"Bad Weighting" even though model seems perfectly posable?

[scurest]

It looks like you've used "Godot Engine's "Better" Collada exporter for Blender" to export, and it looks like it doesn't automatically normalize weights for you. Either use the builtin Collada exporter, which normalizes weights automatically, or you can probably fix it by going through all your objects and using the "Normalize All Vertex Groups" operator (make sure you turn off "Lock Active").

Btw your paths in the .mtl looks like .\\soba_wear_alb.png. It'd be better to do soba_wear_alb.png.