If billboards have negative externalities, then tax those; don't ban them.
So I hope we established that there is a finite tax that's large enough to cover the negative externalities.
Now we just need to figure out what finite amount of taxation is reasonable.
> What's the tax value of "my city looks like a garish parade of bullshit I don't need"?
Different municipalities (and their voters) can differ in how much they value money vs aesthetics. There's no one size fits all solution.