I'm striking out on TFL and yards per tackle ... hopefully others have more luck. I also noticed on an occasion or two above I noted pass plays, mea culpa.
I just don't see a team allowing 78 yards per run, with a guy averaging 10 tackles per game being the "weak link." Even assuming Edwards had only 1/2 of his stops on run plays, 5 yards per run ends up being 25 out of 78 yards... about 1/3 of all opponent yardage... on those five plays Edwards makes the stops on. If you call the average 3.9 yards (the NFL average run play,) setting the bar at 4 yards makes little sense, since that doesn't qualify as a poor performance against the run. But even so, that would mean Edwards accounts for 20 of 78 yards, on his five rush tackles.
So on the other 25 or so running plays, the other team gets 58 yards... that would mean everybody else on SD who records a tackle is doing it two yards and a half yards past the line of scrimmage. And that is assuming Edwards plays middling run defense (league average 3.9 yards per stop,) not that Edwards is bad at run defense. If Edwards is truly bad against the run, the average non-Edwards tackle is a 2-yard stop.
I could easily see this as a situation where Edwards gets to plays he has no business getting to (with 17-tackle games, you have to figure that happens on occasion,) and instead of quitting or not getting there, gets a grab on a guy other linebackers wouldn't have gotten to at all. Of course the physics of launching a smaller body rather than a larger one comes into play too, and your guy can get "dragged", especially when he's making a stop of a big back with a full head of steam.
If that's the tradeoff though, I personally think I'll take it, unless as outlined above everyone else in San Diego is really tackling guys for an average gain of 2 yards per carry. In which case I find the guy that's really responsible -- let's say the one with the second most stops on the SD defense -- and pay the big bucks for him. I mean a guy that can take up Donnie Edwards' slack??? We GOTTA get that guy!
PFnV