Thank you, Abhay for your valuable comments.
I called up Jio and they confirmed that duplicate SIM cards will come unlocked even if your original SIM was locked. So what you said about SIM locking is true - it's a lock on your physical SIM card, and not the mobile number as I had wrongly assumed. So I have corrected my post to reflect this.
As for using Authenticator apps, I have mentioned that you need to remove your mobile number from Google after setting up Authy. Else Google will just send an OTP to your mobile which defeats the whole purpose of using an authenticator app. About Authenticator apps being redundant, I disagree. If I try to sign in to my Google account on a new device, it sends a prompt to one of my other devices which I'm signed in on. The problem is I’m jacked if that device is not with me. Having an authenticator app solves this issue. Please correct me if I'm wrong.
Writing the back up code on paper offers better security, theoretically. But practically speaking, it's not a good idea. People forget where they kept the paper, forget to take the paper when they travel, and sometimes completely forget that they wrote it on a paper! Scanning and keeping a digital copy may work better, but keeping track of that is a nightmare. No man, I recommend an authenticator app to writing codes on bits of paper, and stand by it.
Moving on, if you read my post, you will see I mention that SIM cards were never designed to be security devices, and I suggest SIM locking as better than doing nothing, and ended the SIM locking section by saying it will not keep out the hacker. So I think labelling my post as 'grossly misleading and incorrect' may be grossly misleading. I would favour 'slightly' misleading.
Having said that, SIM swapping is a major worry to people and I appreciate your taking time to comment and improve our knowledge on this subject.