What you say is true. But the counterarguments are:
- At least according to Level3, it was not standard practice in the industry to charge for peering (not transit - the final destination for the packets was in Comcast's network), regardless of traffic ratios.
- You could say that it should be standard practice, but that would be unfortunate because Comcast effectively has a monopoly on fast connections to its own customers. Since it's much easier for consumers to switch video services than ISPs, failing to reach a deal would be much worse for Netflix/Level3 than for Comcast - so there would be little preventing Comcast from charging as much as it wanted.
This was more true in 2010 when Netflix hadn't yet started creating original series. These days it arguably has more leverage due to being the exclusive provider of those series... but it would still be a huge risk, a huge money-loser for them to walk away from Comcast, or any other ISP, and get into a cable-blackout-like situation. Anyway, cable blackouts feel distinctly unlike how the 'open' Internet is supposed to work. Netflix is one thing, but what about, say, would-be competitors to Netflix that currently have few customers and almost no leverage?
- It would also arguably be double charging - charging consumers and backbone providers for the same packets. If you buy "Internet access" with 100Mbps download speed, but that actually means "100Mbps down from companies that pay the toll", are you really getting what you paid for? Admittedly, transit providers have similar practices, but the level of competition for transit makes that less of an issue.
- Also, most Comcast end-user connections have much higher download speed than upload speed, so even if users were saturating their (paid-for) connections in both directions talking to Level3, Level3 would still be sending more data than it received. In other words, rules about sending and receiving similar amounts of data never really made sense for peering between a consumer ISP and a backbone provider, even if this was less visible in the past.