I do absolutely agree with you that ISPs are in a poor state in the majority of the US. I think a lot can be done to improve it. I disagree strongly that net neutrality is the most important or most effective lever to push on.
As I have made clear, and as I think is fairly obvious to anyone who has moved between various ISP markets in this country, I believe that the quality of internet service is positively correlated with the number of providers in an area. I have cheap and reliable internet with three ISPs. None of the three throttle their connections in this market, and one has just introduced 10Gbps fiber to the home. The fiber provider is actively expanding, but even if you don't live on a street with access, you can get cheap reliable service from either of the remaining two.
I think it would be better for any individual in the US who cares about their internet access to move their markets in a direction from one ISP to more ISPs (like the area I live in) than to pass a law enforcing net neutrality and forbidding any kind of rate-limiting.
I do care about ISPs being able to offer me as many types of service as possible, and me being allowed to choose the service I prefer. Again, my general preference is for unlimited internet, but my preferences are bounded by costs. Another hypothetical: Suppose I am willing to pay $15 for internet access, and the only service an ISP is willing to offer at that price is throttled in some way (data cap, certain sites slower, whatever scheme). If you eliminate this as an option, then you have eliminated my access entirely, because $15 is my limit. In this way, marginal customers may be harmed by net neutrality.
I am not convinced by the argument that the internet will be ruined if some internet service contracts are rate-limited in some way. The biggest threat to the next (Google|Facebook|Twitter) is not any ISP, but (Google|Facebook|Twitter) existing and having a large network effect for its services. And to be honest I have not seen much more argument beyond this point. Even if I were to accept this argument, I think the pathetic internet connections that some people in the US have (there are people still on dialup and Forgive me if this is a misinterpretation, but you seem to jump from my hypothetical of _one_ ISP out of >1 in a market offering _a_ plan that is rate-limited in some way (what if it is just a data limit? This does not favor any portion of the web over another.) to there being no un-rate-limited service contracts available. I find this incredibly unlikely, primarily due to the huge unpopularity of rate-limited plans among a vocal minority of internet users.
Finally, I am quite confident that two ISPs fighting for my dollars are more likely to offer me something I want than two ISPs fighting for a favorable interpretation of some regulation.