In terms of specificity, doing weighted crunches/situps/twists/leglifts would be more specific in terms of forces and time (10sec 100m to 50?sec 400m). And I don’t know anyone who has ever injured themselves doing a weighted twist.
My main problem with the ‘thousands’ thing is the time involved 30min/1000. And if TNT’s calculation of 2.5 hours is even twice too much, then that’s still over an hour for a muscle group that is “not biomechanically relevant to sprinting”. Surely that amount of time could be better spent training something that IS biomechanically relevant.