His argument isn't to use worse relievers later in games. His argument is that Rocco used Duran in the 6th and 7th with the 1-6 hitters coming up in the Tigers lineup....and the hitters who have done most if not all the damage against the Twins this week. The bottom 3 in the Tigers lineup are all hitting sub .200. It was a 1 run game. If a manager wants to assume his best arm can get through dangerous hitters in the lineup, it's giving the Twins offense multiple innings to add on to a 1 run lead.
Yes, that means you are still going to face the lineup again, potentially with a 1 run lead. Personally, I would rather see them keep the lead and try and add on rather to just wait and save your pitchers until the end.
Really it's all moot because you can bitch about bullpen usage all you want, but scoring 2 runs in 3 games isn't going to lead to too many wins.