You purchased a package that gives you access to your ISPs network at that rate. Not even the highest business packages will provide an end to end SLA unless you're paying for a leased line from your location to the location you want the SLA for. Once your packets leave their network they have no control.
You're only purchasing access to their network, and their network happens to be attached to other ones. If they weren't connected to a network with Netflix, you wouldn't have any recourse because you're not buying a connection to every computer on the network. Of course, practically they provide access to every site. But that's not what you're actually paying for if you check your contract.
no one is purchasing comcast service just to connect to other comcast customers.
I don't follow. I am a consumer who has purchased an internet service package that advertises 100Mbps down, 10Mbps up, and 100GB of transfer every billable month.
If I, the ISP, have 1000 customers fully utilizing that 100Mbps down between 6-11pm _it is my engineering problem_
Whether it is netflix, google, mlb, or literally anything else. _it is my engineering problem_ to provide the service I am charging for.