I think a clarification would be helpful here. Were they "deliberately undersizing" or were they refusing to to increase capacity to accommodate the surge in additional Netflix traffic without being paid?
This is how Cogent described it, “Comcast refused to continue to augment capacity at our interconnection points as it had done for years prior.”
via: https://qz.com/256586/the-inside-story-of-how-netflix-came-t...
Comcast claims: "Comcast executive vice president David Cohen said Comcast was forced to react when the flow of traffic with Cogent went from roughly equally to Cogent sending five times as much data as Comcast was sending back."
via: http://www.mercurynews.com/2014/05/08/cogent-ceo-comcast-pur...
That's an arbitrary assessment. It is a problem for both sides. Netflix was paying Cogent for bandwidth. Cogent was taking advantage of a peering agreement (peer ~ equal) that was then thrown way out of balance. Netflix switched from paying Cogent to paying Comcast - both sides had obligations to pay for bandwidth from the beginning.
It's not like Netflix moved their servers into Comcast or Verizon data centers and paid for the bandwidth (although they offered and the offer was rejected). How many other internet companies pay the end user ISPs for their peering bandwidth? Why should they? That's what the users are paying for.