Given you responded to a quote about the C8 platform redeeming GM - it'd probably pertinent to specify you're talking about literally a completely different car other than the name. The C8 was a ground up redesign.

That being said, the C7 also had no known electrical issues. A certified pre-owned would still be covered under lemon law. "driving through a puddle" sounds like more than a bit of an understatment if it took out the entire electrical system. I have driven my car through many, many rainstorms and had exactly 0 issues. I'm also not clear how he traded in a car with a non-functioning electrical system, no dealer would touch that with a 30 foot pole.

>the other kept killing the battery at random.

That could literally be anything, and again wasn't a widespread issue with the C7 platform or there would've been a recall, just like with the C8.