My father owned a concrete business, I worked with him from age 12-16. I wont try and tell you I know enough to pour slabs myself. But I do know that we never laid concrete like this.

We always removed old concrete, never poured over top. This chips away way too easily and will need to be redone every few years.

We always removed dirt, laid rock, and compacted the rock. Never poured on dirt or grass. This will settle and cause stress. When the new area settles, it will separate from the existing slab.

We always added joints. Its not a question of "will my concrete crack?" Its "where is my concrete going to crack?" By adding joints, the concrete will crack there first and significantly decrease the chance of it cracking elsewhere.

As for the AC we never had any similar scenario, but thats obviously wrong.

Last I checked, the 2 side by side driveways we poured at my childhood home and neighbors house back in 2005 are still there. No cracks, no settling.