To me, these results are still quite good, because EKWB 240 is not the best 240 AIO. The components that were used for the test run quite HOT and the temps in the C4 are not that far from the baseline albeit at higher rpm and slightly lower clock speeds. Also, no 90mm on the back was used in the classic layout, which might reduce temps by 2/3 degrees. We must also not forget that although this is a premium case, it does not mean that everyone will get the most power hungry/hot CPU and GPU out there. Overall, I am satisfied with the product as it is and I love its design the most out of all the other options out there. I will buy it in its current state if it rolls out, but I would not mind waiting for a bigger version since I will make a new system at the end of 2021 when ddr5 comes out. That being said, I don't want a 280 AIO compatibility if the overall visuals of the case change drastically and couldn't care less about a 3 slot gpu, since I am fine with a 2 slot one, and would much rather have 25mm on the bottom in the classic layout instead of 15mm fans.
My feedback on the current state of the case is that when a person buys the case, he/she may have an option for 8mm or 15mm depending on the desire of the buyer (performance vs visuals). And I got confused about the DUCT BARS; would it be a possible addiction as an accessory or is it something that the user might have to make on their own if they want to?
Personally, I have been in a similar situation when writing a philosophical essay. It would never be "perfect", but at one point I had to submit it and only then could I see real feedback in form of counterarguments. In this situation, no personal testing can account for the myriad possible configurations, which users will use that will paint a more detailed picture of the capabilities of the case. The best solution might be to put the Dan C4 out after some tweaks that are results of this test and then start a project for a 280AIO case version that might be something like Dan C4 280 Perfetto and will adhere to the ideals you have set out for yourself. Look at the Lian Li O11 Dynamic as an example, it was designed by derba8er, but it was still not perfect, so they made a MINI, an XL, and an AIR version.