To this very day, I know nobody - NOBODY - who even comes close to Gmail’s spam filtering capability.
I disagree. Perhaps you need hard evidence for a claim like that.
I have a gmail account, and a proton mail account. My gmail account is packed with spam. It has so much spam its crazy. The account is basically unusable. Which is fine, because I no longer trust google. It's been years since I've told anyone to use this account.
On the other hand, I can count on one hand the number of times I've got a spam message in my inbox on protonmail. In fact, I remember. It's 2. The account isn't as old, but I've used it to sign up for at least as many things. It's my main account now - partially because I've turned anti-google, but also because its not choked by mountains of junk.
(To be fair, I suspect the main reason that my gmail account is so bad is that it has a popular username, and other people have accidentally signed up for things with my email accidentally instead of their own. Nevertheless, the fact is that the gmail is spam-central, and the protonmail account is clean.)
While I disagree that "billions is beyond being halved", there is some truth to the idea that numbers can get so big that halving doesn't make much difference. That seems very very counter-intuitive, so I'll try to briefly explain.
Consider (10^10 + 2). That's 10000000000+2. I think it's fair to say that the +2 doesn't make a lot of difference. It's still approximately 10^10.
So then, consider 10^(10^10)×100. That's a huge number, too big to type here, then multiplied by 100. So the result is 100 times bigger than the huge number. But... writing it down we see this:
10^(10^10)×100 = 10^(10^10+2) ≈ 10^(10^10).
So although ×100 does make it one hundred times bigger... that just doesn't really make a lot of difference to a number as big as that one. As numbers get bigger and bigger, they start to take on properties a bit like 'infinity'. Addition stops being important, then multiplication, then for even bigger numbers exponentiation doesn't huge much of an impact either.
Mathematically, I think this is really cool and interesting. But I don't think 1 billion is that big. 10^9 is big enough that +2 doesn't matter much, but not so big that ×2 doesn't matter.
[edit] (I'm struggling to get the nested powers to look right... So hopefully my meaning is clear enough anyway.)