Our fourth starter in 2022 was Thor (two starts), plus Falter (one terrible start that the Phillies still won). Eflin was in the pen.
Sanchez was not an especially good 4th starter in 2023 either (after he beat out Walker and Lorenzen). We never got far enough to have one last year.
So do you need one? Yes and no.
I'm not sure exactly what they are thinking as far as the NLDS roster in terms of how to use someone who might also be an NLCS starter, but Trivino and Lazar and Mayza are nothing special, the only thing that makes them better potentially is being more accustomed to the role. Mayza would seems a lock as the third LHP but maybe they don't need that with an all-lefty rotation.
And Robertson isn't competing for anything, he's our third highest-leverage reliever followed by Banks and Kerkering (with Duran and Strahm at the top).
Kemp's hardly a lock either, him versus Wilson is one decision and than the loser vs. Rojas is another.
Dodgers have already moved Kershaw to the pen.