He’s 100% right, we saw last season what one Viltrumite could do while fighting another albeit Mark being inexperienced but it still was essentially child’s play for Nolan. If he doesn’t have any feelings towards Mark he wipes Earth no problem in the finale.

Now imagine an entire species who don’t have the same feelings of Nolan and what they could do.

It’s kill or be killed Mark.

As a non comics reader that’s my assumption too, that the books will give Mark the training that Nolan would’ve if he had the time to.