You have depth in case the need arises to exhaust it. When you slide Zach Eflin or Jake Thompson into a starting role, you don’t think about how unlucky you are that Charlie Morton or Aaron Nola has gone down; you think, "Thank god we have someone other than a soft-tossing space-filler to join the rotation in their stead." You also think, "Damn it, what the hell is happening to all of our pitchers."
Baseball features a long, sad season that chews hungrily away at the human body, so the mounting casualty count of this rotation is not ideal, but also not totally unexpected.