I would approach this as a discussion, assuming there is a miscommunication or legitimate change at the root of this, and sit down with the ASM outside of regular rehearsal/running to talk through the backstage track. I’d stay away from telling the ASM that you “really want the job done the way you did it.” Instead, focus on the fact that each task needs to be done, ask questions about what the challenges are, and really listen to the ASMs answers. It is possible the ASM could have an equally good, but different, way of doing things, and I’d be open to their methods as long as they get the job done, since many different SM styles can be successful.
If they have your old run sheet, make sure the notes are clear to the ASM, and be very specific, even if you feel like you already did this or they should have asked about questions sooner. If they’ve made their own run sheet, maybe you can compare it with the old one and explain how, exactly, you were able to manage it all on time in the past. If there is no run sheet at all, that may be the root of the problem, and I’d help the ASM make one. Also, even though it’s the same show every year, sometimes tiny changes do happen, and make a big difference. Maybe there are different actors or crew, or an actor isn’t feeling well this year so their pace has changed, effecting the ASM. Maybe sets or costumes have become worn-out after years of use and are causing problems. If the ASM is defensive, realize they may just be nervous as the show is new to them, and it’s hard to be The New Kid. If that’s the case, do what you can to reassure and support them, while making it clear that certain tasks need to be done, and doing them will get easier with practice. If you have some of the same actors as last year, and have good relationship with them, maybe you can discreetly ask one or two if things are running smoothly for them backstage (don't mention the ASM, but see if they bring him/her up), and if the answer is yes, at least you can feel reassured on that front.
How-much-is-too-much really varies by show. In this case, since you’re not asking the ASM to do anything you haven’t done yourself, I guess the answer is it is not too much in this case. But also try to remember the first time you did the show, and whether things seemed easy or overwhelming to you then.
