How does net neutrality promote broadband provision competition?
That being said I think that net neutrality promotes competition on the internet as a whole, which I think is more impactful and positive, but in this line of thinking is probably a little besides the point.
I don't really think ending net neutrality promotes competition between broadband providers either. I think either way you have entrenched natural oligopolies, just with NN they're not getting in the way of a free and open internet.
Comcast already refused to make infrastructure upgrades so that customers (who were paying Comcast) could get the services they wanted (Netflix). If net neutrality protections are removed, they could just throttle them out of existence.
I, as a one man web dev shop, run about 20 or so websites. Some are info sites, some are SaaS, some are just hobbies. Comcast won't throttle traffic to me because they don't care about someone as small as me -- but if Comcast and all the other ISPs start offering "fast lane service" for cheaper prices that give prime service to big places like Facebook/etc (who can afford to pay the ISPs kickbacks), and degraded or "normal" service to everyone else (me), then I am harmed just the same.