1 IPv4 address hosting a subnet with NAT vs. an IPv6
2^32 = ~4.3 billion
2^64 = ~18 billion billion
So they are only "roughly equivalent" if by that you mean "within 10 orders of magnitude of each other".
I think you meant "one IPv4 Internet (4.3 billion hosts) where each host NATs an entire IPv4 internet vs. one IPv6
In practice you can't assign anything smaller than a
-- snip --
It's still way more address space than we'll ever reasonably need, but not quite as ridiculous as it looks at first glance.
While true, you will get that