while this is a good technique for certain cases, it wouldn't work in the case of leech people, because leech people are leeches by birth. They get born without the divine sparks that make up real human beings: compassion, understanding, the ability to discern and do good, empathy, etc.
The leech people are shallow, but - as mentioned in this video - they're also evil and manipulative (and - sadly - they're very good at this) that - for weak or uneducated / unaware people - they're really hard to spot and handle. I know this because I am one such weak / unaware dude that's being acquainted with several such people that I have always disliked and tried to avoid but could never figure out why I need to avoid them until today.
What you're describing in that 5 whys example relates to codependent people which - a lot of times - can be mistaken for leeches since both types of people share common traits. But codependent people can be fixed and - most of the time - are normal people because they do get born with human qualities, they're just being the victims of circumstance or nefarious systems acting upon them (society, family, working entourage, the government, etc.) So these people can be fixed and brought to normal. But leech people can't! They get born without spiritual and intrinsic components that make up the human being, which is why you shouldn't try to reason, or deal with them. Again, I can name at least 3 such leeches that I am "friends" or acquaintance with, and they can't be reasoned with, so I have 1st hand experience with them. With such people you either have to cut ties with (permanently and completely), or make it obvious to them that you've figured out their nature and once you do this they'll leave you on their own (well, most of them anyway)...
So yeah, avoid such people at all costs as they live off, and thrive on feeding on your lifeforce / vital energy. Your life's entire purpose is to keep them alive and thriving, which is not good for you as a good man because the more good people are being kept from manifesting their true nature because of these parasites the worse life is for the rest of the good people, which is part of the reason for which our society and lives are so miserable....