I don't notice Marlon's tackling all that much, because teams avoid throwing his direction. He's that good. I'd complain about something else when it comes to the defense.
I'm certainly not putting him on the level of Queen's ineptitude and you're right, he's really not involved on that many plays relative to the greater scheme of things but there are plenty of times where he's so determined to punch the ball out, he gets careless with tackling. I've seen him ride the back of a receiver for several yards more than once. Compared to some on this defense, I guess you could say he's one of the better tacklers but that's not saying much.