Most grapplers try to fix a strength and gas problem on the mat, with extra rounds and every open mat they can make, hoping the engine shows up. What that teaches you is how to roll tired. You drill the bad positions you fall into when you're gassed, and you pick up more injuries doing it.
Strength that lasts deep into a round, the muscle behind your grips and pulls, and top-end strength for scrambles are separate qualities, and rolling alone won't max out any of them. As Tod's program notes put it, grappling conditioning comes from "sequencing adaptations so each one is built on top of the last."
Combative Strength builds all three across its three phases, then tests you before the last phase and again at the finish, so you can see what moved.