Ok have fun performing psychological experiments on your brain using "informal" merriam webster definitions
You're just being pedantic and grasping at straws. Whether or not we're using the scientific term for an individual's mindset (which is not quantifiable to a high degree of precision but that doesn't meant it's not quantifiable at all, you can at least reduce most 'measurements' to a binary range) is irrelevant to its significance. The comment you replied to specifically said it would be hard to do a rigorous study of.