"And he has zero chance of winning, so what's the point of voting for him?"
It's a protest vote...much as is a vote for Trump.
"I would argue that a vote for Johnson is basically a vote for Trump."
And I wouldn't take the bait. :-) I would, however, suggest that how such a vote would be 'wasted' depends on the beholder. There are many who see a vote for Johnson as a vote for Hillary.
You're asking the wrong person. I don't vote for the evil of two lessers. I do not legitimize a broken, corrupt and barbaric system by participating in it. YMMV.