I do not think this is a valid argument. Especially coming from the Indian government, who has at many times cited security and safety issues to curb internet freedom.[1][2]

[1] https://en.wikipedia.org/wiki/Internet_censorship_in_India

[2] https://www.bbc.com/news/articles/cn074j04l3eo

I had a feeling this wasn't too well thought through.

It makes it easy to claim another person's identity, while at the same time, well-known people likely wouldn't want a username that makes them easily approachable to strangers that otherwise woudln't have their number.

I am not a known person but I still have no incentive to pick a username. Someone wants my number, I'll give it to them.

For a medium like Twitter, usernames are an obvious feature. For DMs that were previously number based, not necessarily.