Well, I’ve seen all sorts of claims, usually without data to back them. One source claims that only 38% of households actually has competition, although it didn’t cite sources. It’s possible my info is out of date. And that could easily be due to various ISP’s going out of business or buying each other up (due to “net neutrality”).
(But are you sure you don’t have both a phone-line choice and a cable-based choice?)
Consumer “last mile” shouldn’t be allowed to block anybody. There should be no way legal or other impositions should force it to. In general, any blocking an ISP does at that level will be either in restraint of trade (forcing you to use their preferred vendor, which violates anti-trust laws) or because somebody has threatened them with legal or other harassment.
Whatever their reasons, an ISP risks considerable administrative/legal expense if it is accused of such blocking, even if they’re innocent, which means they usually won’t do it without a good reason. Of course, existing competition that customers can switch to is an additional reason not to.
Throttling is a different issue. Every ISP has at least one connection to the wider Internet “backbone”, and such connections can get overloaded. In addition, local subnets can have limited bandwidth, and can also get congested.
When this happens, the ISP has to have some way to limit traffic. If it doesn’t, it can experience congestive collapse. Such throttling can be done in many ways, but however it’s done, somebody’s going to be running verrrrry slooooow.
Because parts of the general “backbone” can also become congested (or even drop), most ISP’s will have several connections to different parts of it, which may have different bandwidth, both at the connection choke-point and within the wider “backbone”. Each connection has to be paid for, at different rates, for the connection itself, packets sent, or both.
Some proprietary high-bandwidth links could limit traffic by “edge” service (e.g. Netflix), charging high(er) prices. If the “edge” service is paying, the ISP might not have to, which means even “monopoly” ISP’s would have an incentive to use them, although only customers of the “edge” services would see traffic through them.
This was prohibited by “net neutrality” (AFAIK), partly because companies like Netflix wanted to get their high bandwidth for free, while their competition was prohibited from paying for bandwidth to provide better service.
This, IMO, was the major problem with “net neutrality”: it was a heavy-handed blanket prohibition of many types of innovative solutions beyond the “last mile”, which has slowed the growth of technology and investment in infrastructure. (Others point to the fact that it allowed all sorts of content censorship by the FCC or anybody who could pressure it.)
Something to keep in mind: available services over the Internet are continually growing in their bandwidth requirement. The same service that worked fine a few years ago will probably be slow and cranky today. Good connections require continual investment in new and better equipment. And somebody has to pay for those upgrades.