They are trying to get weight back down for fuel economy, so the manufacturers make things as thin as they can and still hit the payload and safety targets. So while the roof is thin, I bet it would hold up in a rollover as well or better than previous years.
I do personally agree that effective quality appears to be down compared to the GMT800 era, but only in some ways. The new door design seals better, has less road noise, etc. But the electronics are more issue prone, IMO. Not just GM, Chrysler's
UConnect is having problems right now lol
I wish manufacturers would take more time to polish the user interface software of their cars. But in terms of the mechanical aspects of cars, I agree with Dozerboy, they are getting better, not worse. That doesn't mean they are perfect, or that it is even a better experience overall. (The poor overall experience is why I sold my 2013 Cruze and got a 1998 Pontiac to replace it. Compared to my 2003 2500HD, the 2013 Cruze was a cheaply made glitch factory.)