It's no less true for cold-potato routing; the source is just closer to the endpoint. And CDNs doing cold-potato routing happily pay for their transit because the service THEY make money off of is providing CDN services to their customers, who theoretically make money off the content they pay the CDNs to distribute.
What it comes down to is Comcast has no incentive to ensure its routes to various Internet transit providers are GOOD if they're not monetizing them. Why should Comcast be treated differently than any other transit provider and not allowed to monetize its transit services? Netflix wasn't paying Comcast, so Comcast had no responsibility to help Netflix make its own service better when there were other ways Netflix could have alleviated the bandwidth situation (e.g. buy transit through another company).
The original L3 article actually touches on this, sort of, by mentioning markets where ISP port congestion is not an issue (i.e. the UK) due to competition between ISPs.
Comcast will get paid by their customers as long as the routes they pass traffic through are 'good enough'. They have a (near) monopoly on the last mile in many markets, so 'good enough' can mean both 'barely working' and 'better than any other option you've got' at the same time.
So, you're right, but so is the parent: Comcast has no financial incentive to provide any more than just enough bandwidth to keep you from calling the support line to complain or cancelling your contract in frustration.
What it comes down to is Comcast has no incentive to ensure its routes to various Internet transit providers are GOOD if they're not monetizing them. Why should Comcast be treated differently than any other transit provider and not allowed to monetize its transit services? Netflix wasn't paying Comcast, so Comcast had no responsibility to help Netflix make its own service better when there were other ways Netflix could have alleviated the bandwidth situation (e.g. buy transit through another company).