I call bullshit. And I call it bullshit because I've done both, with transitioning Fantasy Magazine from print to online. (And I've seen the slush for Weird Tales for several years). I was a bit apprehensive, at first, but I actually found the following to be true: 1) the number of submissions, statistically, did not go higher, and 2) the quality of the submissions actually got better. Yes, you heard that right.
Consider this: for the print edition of FM we would get paper manuscripts from inmates, from little children, from whackjobs, in various formats and layouts and god-knows-what-else, and it was pretty bad stuff. The chance that I would find two great gems in that great slushpile was pretty slim. And it just ate up time to go to the post office, get the envelopes, open them, respond to them, mail them back, it was just a big waste of item and energy.
However, with the online submissions I'm far more likely to find four to six, or more sometimes, every month. And possibly one of the reasons why the quality might be higher is that the magazine is out there, online, for authors to read, which helps them to determine if their fiction is right for this venue. On top of that a lot of writing workshops are very much attuned to what's going online, and are more inclined to submit. Quite a lot of the online submissions I know for a fact have workshop credentials.
The idea that authors mailing out paper submissions somehow are better "invested" than authors submitting from online is just nonsense.