Net neutrality
regulations were adopted to protect (and in some degree restore) the net neutrality
condition; the internet was largely neutral from its inception; though by the early 00s threats to neutrality in practice were becoming clear, and the FCC began discussion the issue, adopting open internet principles that it first attempted to promote via case-by-case action (which was limited by the courts), then Title I regulation (which was struck down by the courts) in 2010.
There's considerable reason to believe that even without enforceable rules, the attention and active policy activity directed at enforceable rules inhibited non-neutral action by ISPs compared to what it would have been without that activity.
> So to say that Net Neutrality has been key to an open internet from 1980-2015 seems without merit.
To say net neutrality regulations have been would be without merit, sure. To say net neutrality has been, OTOH, is factually true.