Grant does not say that a stop conditions the gelatin. What he does say is that a stop is important for uniformity and for maintenance of fixer activity and he does say that it is better than nothing at all and better than just a rinse.

He has nearly a chapter on this and it is permanently marked in one of my copies of Haist. Now, taken out of context and paraphrased, one might write that the gelatin is conditioned, but this word covers such broad territory, it could lead to another "myth" about analog photography!