I'm not "basing any theory" on anything. I'm telling you, objectively, that side button touch ID is terrible. It doesn't matter if you want the foldable. It doesn't make side button touch ID any less terrible.
Touch ID worked fine when the iPhone had a Home Button because you needed to touch that anyway. Now the same natural gesture, that was already required, authenticated you with zero additional effort.
Face ID of course blows that away because all you have to do is look at the device, which you have to do anyway in order to...you know...use it. A fact that is somehow lost on people obsessed with unlocking it in their pocket or otherwise not in their hand.
I can see by your last sentence though that this is going way over your head.