It's my understanding that interconnect agreements solve congestion on the network by having a larger connection to infrastructure.
Fast/slow lane practices throttle that connection, regardless of how large the pipe is.
So, my small business website could be using a large internet connection that technically has plenty of bandwidth to carry my traffic but, unless I pay Comcast a premium, traffic from my website will be put in the slow lane and throttled back.
Then your understanding is incorrect (sorry; not trying to be flippant). Interconnects are the entire story here.
The media has framed a lot of the congestion issues in the context of "fast/slow lane" but what they come down to are business disagreements between the transit providers and the ISPs. The solution to these disagreements from the viewpoint of a large service provider is to purchase an interconnect directly to the ISPs. If you are a small service provider, the solution is to purchase delivery through a CDN. Netflix used to purchase delivery through CDNs until it got too expensive for their business model; so they started building their own CDN that they called "OpenConnect". They used their positive brand image in conjunction with the ISP's poor brand image to launch a PR campaign with the goal of knocking down the price they would have to pay for interconnect service. It worked; they knew they were always going to have to pay the Comcasts and Verizons of the world but they were able to talk the ISPs down a significant amount.
Strategically, it's a bad position to be in for a service provider because the ISPs can raise the price at any time (which is why Netflix has continued complaining about it). But realistically, the ISPs sit on such a strong market control point that nothing can really stop them from setting prices (common carrier status just means they have to offer the same price structure to everyone; not that they can't arbitrarily raise prices).
Fast/slow lane practices throttle that connection, regardless of how large the pipe is.
So, my small business website could be using a large internet connection that technically has plenty of bandwidth to carry my traffic but, unless I pay Comcast a premium, traffic from my website will be put in the slow lane and throttled back.