If Mark is the Mole, more than likely we'll learn that he: 1. did some sabotage that viewers wouldn't be able to detect; 2. tried but ultimately failed to sabotage in many moments; 3. found himself in bad positions for sabotaging.

I still think it's quite possible that mid to end game too many players were on to him and watching him like a hawk, and as a result he found himself unable to sabotage without it being obvious.

But all you MarkFOMO-haters are right, unless we get some crazy revelations at the finale, he wasn't a very good mole.