I’m not aware of evidence that proves Edmunds “isn’t good” shooting the gap, but I’m quite certain he isn’t asked to play that role. If anything that’s what Milano, Klien and even Poyer do much more often.
As you note, Edmunds is a superior space eater in pass coverage, which is his job. Fans say Edmunds doesn’t have “good instincts” but he doesn’t play down hill, he plays a step back and then sideline to side line - not shooting gaps.
Saturday’s goal line plays illustrated this well.