This is my experience. While transient mode helped at the beginning for discovery. I learned fast the 10 things I use constantly, and never look the transient buffer. When I want to do something, I see the documentation, for me it is often easier than guessing and searching. Things like spin-off are absolutely gold.
(I'm the author of Magit and Transient. (Though not the original author of Magit.))
The transient menus certainly play an important role but I think other characteristics are equally important.
A few years ago I tried to provide an abstract overview of Magit's "interface concepts": https://emacsair.me/2017/09/01/the-magical-git-interface/. (If it sounds a bit like a sales pitch, that's because it is; I wrote it for the Kickstarter campain.)