>>5959267nta, but I'll confirm that sketching in inks will improve your drawing skills. It makes your lines much more accurate and confident over time because you have no safety and you have to live with each and every line you put down on the page, so it's constant do-or-die, and if you wipe out, you just start over. Then, whenever you draw in an erasable medium, that same balls to the wall attitude will carry over into that.
Peter Han (whose Dynamic Sketching course is more or less what DAB is based on in the first place) recommends drawing in inks in his course. Scott Robertson also says the same in How To Draw. It's definitely not something Irshad came up with, he's just parroting what a number of other people have said already.
I myself didn't start sketching with pens on anyone's recommendations, I did so just because they felt so good to draw with. Never went through DAB either, so I'm definitely not an Irshill from r/drawabox.
