Is this a deliberately confusing explanation? "... this falsehood perpetuated on the big screen in Quentin Tarantino's Django Unchained where the eponymous character spells his name, adding 'the D is silent'." ... "The D is not silent, it's very much pronounced." ... "... Tarantino's film teaches the correct pronunciation ... it is incorrect to say 'the D is silent'." ... "But in French, /dʒ/ can be written 'dj' beca…
/dʒ/ doesn't have to be be written "dj" (it isn't in English, for example). It just is written that way in French because "j" alone is just /ʒ/ (as you quote above). When you ask "why not just say...", well that is pretty much what I say in the first sentence of the third card.
#1: You preface that sentence with "But in French" so why mention English? Can /dʒ/ actually be written some other way than "dj" in French? From your post, it seems like the answer is no.
#2: The first paragraph of the third card neither mentions nor implies (to the non-linguists among us, at least) anything about English "j" having a hint of "d". This is something I'd never realized before, and only discovered it by saying "James" aloud a few times after this post; and I'm still not 100% sure that it's right, based on the post.