I agree. It would be great if articles such as this provided information related to the average energy cost of producing a pound of each kind of meat, and other environmental impacts of a per pound basis. Including transportation, refrigeration, etc. To take that a step further, a comparison of mass-production to local-production would be interesting. All of this information is out there, however, many articles don't dive into that side of things.
...I'm not defending the article for what it isn't. It's very clear that it's not a reference and data heavy article, and was agreeing with the points you raised. There are pros to each, and this article was based around people's perception of what impacts climate change, showing that many people don't have an understanding of it. The point wasn't to say "here's all the data you need" it was to say "most people don't even know what data they should be looking at".
It's all good, we seem to agree on the importance of data to back up these kind of claims. You could do the same kind of modelling with water usage (reducing by N units saves O units of water).
I think that The End of Food and The Limits to Growth are a great start!