Well......a couple of thoughts here, the first being no one knows for sure if a compression test took place.Not saying the tech is good or bad......the OP found the car ran well for the first section of his ride home......obviously the tech. had the same experience.
Since none of us have a crystal ball, the future of the service success was unknown.
i am certain you know more about engines and how to repair them than I do. I just don't get not doing a compression test on this car when it has such chronic problems and it is using oil. Why replace all of the other stuff it has a bad cylinder that is causing it to use a lot of oil.
Many mechanics, myself included, perform a test but if all is in spec we don't record our findings.
This may have been the case (speculation)
Since the car ran well, the compression had to be satisfactory since, if there had been a out of spec cylinder it would have run poorly at all times.
Compression, or lack thereof, is a mechanical failure that does not momentarily get well, but can be a fooler.
Example: First, we have three rings per piston....the top two are compression sealers, the bottom is oil control and has nothing to do with compression.
So, the focus is on the top two rings.
I have had engines (this is race stuff btw) that had collapsed ring lands and broken top rings pulling perfect compression numbers.
Speculation, on my part, the top ring was doing nothing and the second ring was doing a stellar job of sealing.
In this scenario, I end up with an engine that idles fine, displays no blow by, and operates well.......untill I stress it by deep throttle/high rpm operation......that single ring is unable to hold the additional cylinder pressure by itself and the thing falls on its face.
So, I light foot it back home, and it is running fine by the time I get back.......teardown is now my only path.
In this cars case, since chevy is calling the shots, I suspect teardown will (finally) be authorized.
Anytime warranty is involved, the real potential of too many cooks spoiling the broth presents itself.....and the customer loses faith in the car/mechanic/shop.
For now, don't yet put the tech. on the hook.