Sorry for not keeping up, but you're a preloader, right? Not in management?
If so, it's really not your job to train new hires. If you're cool with it then sweet, but if it's adding additional BS that you could do without then you should point out to your supe it's not your job/you don't get paid to train employees, and if they continue to direct you to do so I'd try and see if there's something you can work out with your steward. I don't think you'd have a grievance, I just know that the stewards in my center are my most valued resource on the odd occasion where management seems to really be trying to
me over in one way or another. They've helped me sort through supervisor BS so fast that, in retrospect, the situation always seems laughable despite how heated I can get in the moment.