I would go further and say 3b is an order of magnitude too large. Bots aside, If there are only 3 accounts per user, our estimate is at 1b. Now, we take into account malicious agents like bots and spammers, easily carrying a bloat factor of 3-5. The closer estimation might be 100s of millions of unique human users, and maybe half of those users actually care.
TLDR+Edit: Didn't see your other post and accidentally straw manned you. Anyway, I agree it's gonna be "a lot lot less" than 3b unique human accounts.
Well 'smaller' and 'close to 50%' will have different effects, and I'm willing to bet that the number of individuals affected will be a lot, lot less than 3bn.