Debate alert: "Rebuttal to the 'Section 27 of the Evidence Act is always in favour of the person who stands to gain' theory

Kuch toh galat hai, yeh baatein! I've been hearing this claim from my seniors for years now - that Section 27 of the Evidence Act is a magic wand that always saves the person who stands to gain from a contract. But, seriously, koi logic dikhao? This theory goes that if a document is in favour of the person who stands to gain, it will always be presumed to be genuine. Na ruke, I strongly disagree.

What about the facts of the case of Rattan Singh vs. Joginder Singh (1976) 2 SCC 167? Here, the plaintiff claimed a loan of Rs. 10000 from the defendant, but the document in favour of the plaintiff was held to be a forgery. And what about the case of Smt.