Hello @sguyader,
I totally agree with you as regards the difficulty of approaching Rawtherapee at first sight. It is such a powerful tool, with so many options that it may be indeed quite overwhelming at the first approach…
I have started working with Rawtherapee when it was still a freeware, only available on Windows, but I do still consider myself a beginner…
Maybe its “difficulty” is one reason why there are so few tutorials on YouTube compared to Dartkable…
As Darktable is concerned, in my personal view, it is judged more easy to learn mostly because its GUIs is much more similar to Lightroom. Consequently, many photographers and advanced users are alreaday accostumed to both workflows.
As far as I am concerned, I do find the Rawtherapee interface much more professional compared to Darktable. It is not a case that, with the 2.7 version its GUIs has been vastly improved by Aurélien Pierre…
Another improvement for future releases of Rawtherapee might be having a GUIs to chose easily our own preferred tools [1]. Now you must write into a text file to select them, which looks quite complicated (“nerdy”) for the casual user…
As for your suggestion: “on first launch and opening a image in the editor, all the modules are unfolded, showing all the controls”, be ready to be surprised because…
On Linux Pro, an Italian magazin, this year, a contest among 5 graphic softwares (gimp, darktable, rawtherapee, lighzone, pixeluvo) has been proposed, trying these 5 applications with many tasks (each one with a final score).
As regards the best GUIs Rawtherapee has been judged better than Darktable because its tools are already unfolded which is somewhat different from what you are proposing, as regards the underneath controls…
Here is a screenshot in Italian (I am sorry about that but as a French I am sure you are able to undertand it…):
In all truth, I think that all comes down to personal preferences and taste.
IMHO, it is vital to read the manual (e.g. RawPedia) before approaching a professional software. And yes, I am fully aware that most users do not follow this principle at all!
Unfortunately, with open source software there are usually very few developers, at hand, to improve the GUIs. Even worse the documentation is quite often lacking many parts or, worse, quite outdated (but again, with Rawtherapee, the RawPedia web-page is quite accurate on the whole, IMHO)…
But, to conclude my looong rambling (sorry about that…), I do agree with you that there is always room for improvement as regards the GUIs!
I am hopeful that the recent fork of Rawtherapee [2] may be useful to explore all avenues. By doing so, both softwares are going to improve, in the long run 
[1] GUI for adding tools to Favorites tab · Issue #5256 · Beep6581/RawTherapee · GitHub
[2] My take on RawTherapee