I think that your observations show that technical solutions
will never stop spam. As you point out, it gets redirected to
the technically less savvy and/or causes the spammers to change
their strategy in a never-ending arms race.

If everyone accepted email only from trusted SMTP relay servers
which charge a fee for use (peanuts to a normal user, a very small
cost item for someone who legitimately has many emails to send, too
much to make spamming worthwhile for a spammer) and block access
from those who attempt to spam (if they do so despite paying the fee
and agreeing to abide by the terms and conditions which of course
prohibit spam), then spamming would become so unprofitable that
it would stop.