Part of me does suspect Mark's introduced to fill in the space that Kenzi left behind, also.

I thought of that as well, and if that's true then it's completely unnecessary given that Tamsin is already doing that just fine with her teaming up with Bo and whatnot. And I agree, his presence is a poorly timed narrative choice. He adds nothing substantial to the plot, he only ever fucks up and is childish with the way he acts, and what else is there to do beyond that? It's basically the Rainer situation all over again, and I don't like it.