If the replacement show gets 1/5 the ratings, but at 1/8 the cost, CBS will take that as a win.I assume that you're referring to the replacement programming in the late-night slot, not CBS's overall schedule. In their overall schedule, they do have prime-time programs that get those sorts of numbers, and they have sports broadcasts that do more.
But for late night, I agree with you. My suspicion is that "Comics Unleashed" won't manage to get even half the audience that Colbert routinely got. But CBS knows that, which is why the deal with Byron Allen has Allen paying for the time slot instead of CBS paying for his shows.
It's the basic MBA mindset. Particularly when an industry is declining.