Agree and disagree. Depends on the aircraft type. There are different checklist types.
You are referring more to the airliners. There, you often have the the normal procedures, which is what you do and the checklists are challenge and respond and only check the most important statuses after you finished your procedures.
In GA for small aircraft you often have read and do checklists. Thats like a combination of the normal procedures and checklist. So nothing related to Sims but actually like that in real life. For the airliners I think this is untypical for normal ops. Read and do can often be found in the abnormals.
Memory items are in both worlds mostly the emergency checklists.
But as this topic is about Fenix, I agree with you, the AFM gives instructions what to do and the checklist are typically short of the challenge and respond type. It‘s not like following the checklist covers everything you need to do but you do your workflows and check with your checklist, that you covered the most important things.
Regarding the single source of truth in the AFM: I fly historic aircraft IRL where checklists don‘t exist at all in the handbook an normal ops is more like reading a novel, so even there it‘s not like there‘s one single truth in general. We have Checklists that are developed by our own because at the time the handbook was written, checklists were not a topic 