update for reference:
The issue was that Godot doesn't give you control of the pivot offset (and probably other controls) through the code of nodes I created and set the values for dynamically from the scene itself. I had to make a separate scene to create instances of these buttons from; where all these settings are already applied to an existing button.
Guess that Godot isn't built for certain more complex nodes like textureButtons to be created dynamically. If Godot had thrown an error instead of allowing me to create these nodes dynamically in the first place, i would've figured that wasn't the way I was meant to do this sooner.