Well, I do have a Discover IT card (I've had it for decades, though it wasn't IT until the last year or two), and in the past 2 weeks each week I've gotten junk mail from Discover, one for 0% interest something, and one for their savings account.

So maybe your frequency of Discover junk mail can go down a little bit when you have one (if you had a very high frequency before), but you still get a lot of Discover junk mail if you have one, so getting one does not get rid of it.