Unfortunately, we can't change this behaviour in the Animation system.

Animation Rigging relies on the animation mask to decide whether or not it should read values from the scene (when values are not animated), or use the animation stream (when values are animated). However, when writeDefaultValue is set to false on a state, the animation system will force the animation mask for all properties, thus, forcing the animation stream into Animation Rigging.

Changing this behaviour now in the Animation system would break existing user workflows.

As a workaround, you could write a custom constraint to sync in scene values in the animation stream before evaluating the rest of your rig.