I was going from memory on the 20:1 thing and I was wrong, but 5:1 is still not even close to symmetric.
I also used a bit of hyperbole in the "why do transit providers even exist" part; transit providers do still need to exist to provide access for the long tail. But Level3 and the like do see their market shrinking as the big fish who currently pay them for transit either directly or indirectly move more bandwidth to direct connections with the big ISPs. It is definitely starting to squeeze them.
As far as the benefit to each network goes, that's hogwash. It's not how the contracts are written because you can't quantify "benefit". You can quantify packets sent/received. Netflix needs to make money just as badly as Comcast does, so the fact that their service is crappy is much more their problem than it is Comcast's. Netflix can always purchase transit through another company that's not Comcast.
I can assure you that L3 and Cogent are not seeing the marketplace shrink. 10k quarterly files from each discuss their growths and vulnerabilities.
Historically, eyeball networks have paid for transit from backbone providers. As market consolidation occurred, the cable providers with government granted physical monopolies were able to negotiate for better settlements with their transit providers.
Eventually, the cable companies condensed with the major telephone companies. Some of the new mega companies have backbones and can use their own networks for transit (Verizon, AT&T, ...) others (Comcast) were able to use their size and access to their customers to negotiate largely settlement free exchanges.
However it is important to note that ALL eyeball networks have 1:5 to 1:20 demand ratios. This is the nature of content versus consumption. There is no new news regarding these ratios, and they are not particularly germane unless attempting to engineer the flows.
The real and pertinent issue is that Comcast has not lived up to the 'timely upgrade' clauses in boilerplate (NDA'd) settlement-free peering agreements. Clearly they have an advantage to "defect" from the standard cooperation model. Netflix has chosen to change providers several times, and recently provided data on whom they pay for service.
Why should an end-user ISP ever expect a settlement-free peering bandwidth graph to be symmetric? The important question is whether customers are requesting connections that route through through a particular transit provider. Comcast gets to sell "Internet" access, while the transit provider gets to sell bandwidth. Win win, no symmetry needed.
I also used a bit of hyperbole in the "why do transit providers even exist" part; transit providers do still need to exist to provide access for the long tail. But Level3 and the like do see their market shrinking as the big fish who currently pay them for transit either directly or indirectly move more bandwidth to direct connections with the big ISPs. It is definitely starting to squeeze them.
As far as the benefit to each network goes, that's hogwash. It's not how the contracts are written because you can't quantify "benefit". You can quantify packets sent/received. Netflix needs to make money just as badly as Comcast does, so the fact that their service is crappy is much more their problem than it is Comcast's. Netflix can always purchase transit through another company that's not Comcast.