Yes that does make sense.
The brown goo on the sponge is mainly organic waste (uneaten food, poo, bits of dead plant) with only very few bacteria in it. The bacteria we want attach themselves to solid surfaces with biofilm, and it takes a lot of hard scrubbing to dislodge them. Squeezing a sponge hard won't dislodge them, just remove the brown goo. The sponge will never go white again, though, and if you squeeze it so hard it does go white, that is too hard
With substrat pro I just leave the grid on top of the basket, shake it in old tank water, lift the basket out to drain it, then repeat until the water runs cleanish. Shaking the basket doesn't count as hard scrubbing either.
I leave the grid on top because finding all those little white balls in the bottom of a bucket of dirty water is not easy, and no matter how careful I am if I don't use the grid some always escape
