Even though I can only pull 190, my grip feels like it has another 50-60kg in it at the moment. Mixed with chalk shouldn't leave anyone with grip issues. There's no one who I have taught that grip to from the start, who has grip issues. I imagine the only ones who would have grip issues with only chalk and mixed grip, are those who have depended on straps for a long time.
There's simple evidence in Markos' clients...not all of them are pro powerlifters, but I doubt he would have anyone using straps on deadlifts, and his interest is in getting people as strong as they can be. Dependency is weakness. It's a fake kind of strong IMO, if you can't do the lift without the dependency.