Wide generalizations? Have you read the forums? If you have to disable a key visual component of an OS in order to get rid of lag, you have to agree there's an issue.
His point is just what you have illustrated in this response. There are plenty of threads and videos out there showing zero lag with all transparency turned on as well, and it has been hypothesised that the OS UI lag is actually not a problem with the hardware, but with the software, and it has been a documented problem on ALL of the rMBP's as well as the rMB. But you seem to be ignoring all of these and only seeing the one's that are similar to your experience.
Nobody here is saying that the rMB is a match for the rMBP's or even the 2015 MBA's - I think all of the honest posters here will readily agree that we are talking about a fanless core M CPU design. Even as well implemented as it is by Apple, it is never going to give you the same performance for most of the use cases you are describing and that you use it for (correct me if I am wrong, but have seen you active in most of the gaming and photo/video editing/encoding threads here in the MB section of the forums).
Nobody is disputing that. However, what most people here appear to be pleasantly surprised about is that the rMB exceeds their modest expectations, and feels on par with its more powerful siblings in most everyday general computing tasks, while performing better than expected doing the occasional heavy/intensive stuff like video transcoding, and some photo work.
Again, I don't think anybody here is saying it equals an rMBP for this stuff, just that it performs better than expected and adequately for what it is.
For example, the HD5300 in the rMB is actually more capable an iGPU than that in the 2013/14 MBA. However, it will get throttled a lot when pressed for probably anything more than 30sec at a time, and performance will be significantly impacted by that.
For what the machine is intended for, it in general provides an experience on par with all Macbooks, but you do have to be thoughtful about what your use case is going to be on a longer term, amd you can't come in expecting this to be a jack of all trades. In the Retina category, that is going to be your 13" rMBP. If ultraportablility and office/web productivity is your game, then the rMB is an excellent choice. If you are going to need a machine to be your primary computing device, and do everything from satisfy a gaming habit to being your Blu-ray disk burner to managing your DLSR photo library to being your band's music editing studio workhorse, then the rMB is a very bad choice.
I'm actually not even sure what you are trying to argue anymore. Is your opinion that the rMB doesn't even provide a good enough basic experience to fit in the Macbook line-up at all? In that case I will have to join the many who thoroughly disagree with that opinion. If you have massive lagging issues and feel your computer is unusable, you should take it in to an Apple store and see what they say after showing them the problems, and either get a replacement or trade up to a 13" rMBP. If the machine is faulty it doesn't matter if the two week period is over.
However, if your opinion is that the rMB should perform on the same level as its more powerful siblings in the heavy computing use cases noted above, then I would say your premise and expectations are entirely false and unreasonable in the first place.
Kind of like when I painted my car red.. it just feels faster, man.