I agree with that to an extent. We always seem to be reluctant to put crosses in when Llorente is on the pitch despite it clearly being the best tactic for him. With Janssen, I always thought his hold up play was good....though thats more of use to a struggling team which needs to get up the pitch more. He can finish, its just his movement was cr*p and given we usually dominate possession, we need forwards with good movement to drag defenders around.
All that said, I'd much rather a chance drops to Janssen's feet in the box than Llorente's, so I dont see us being weaker if we player Janssen rather than Llorente