Seems like a strange claim, considering many sites that new internet users use will not let you sign up without an email account

I agree. I'm skeptical and would like to see what data might support that claim. I've not been able to find any myself.

1.2 Billion Whatsapp users with phone number only

800 Million Messengers users as phone number only

20+ Apps with 100m + users as phone number only.

Together these PN based winners outstrip the combined usage of almost all web apps. I mean you are all downvoting me -- but its kind of funny how out of the loop the thinking is here.