I think it's my ISP's job to provide the advertised bandwidth between me and exchange points which offer access on fair, reasonable and nondiscriminatory terms.

My nearest exchange point is probably London Internet Exchange. If an ISP advertises X Mbps, and Netflix can deliver X Mbps of data for me to the exchange point, it's my ISP's job to get that X Mbps of data to me.

No, merely to every destination that can support those speeds. I'm pretty sure YouTube qualifies.

And really, I'd be happy with a mere 10Mbps to YouTube, if for some reason full speed is too hard.

It is Verizon's responsibility to make a reasonable effort to provide that 300 Mbps to the Internet that the customer paid for, especially as content providers are bending over backwards to give Verizon that capacity for free.