have positive reviews destroyed games?

There are two aspects to this point to address:

• Are games "destroyed"?: There will always be people making cool games in the same way that people will always want to make art. If you look at the releases from the largest studios that get the most public attention, maybe you could chart a downward trajectory in quality with some exceptions. In general capitalism kinda ruins everything, including the arts. When profit incentives are prioritized over all else, it's not great for the outcomes. As the games industry continues to mature, there will continue to be cyclical massive layoffs, less investments in innovation, and more reliable "safe" bets that often results in bland content. Again, even within such a system, independent and smaller developers will always be making good stuff. The more the community embraces and supports independent development, eschewing AAA titles, the better the health of the art from, IMO.

• Are there lots of positive reviews for bad games?: Certainly. I think this is more a symptom of the games industry maturing as a capitalist enterprise than a cause of bad games. Many review sites have a business/engagement model that requires they release reviews as quickly as possible, and so depend on access to advance review copies. Big budget studios aren't going to provide early review copies to sites that might give them bad reviews when there are plenty of sites who basically guarantee that they won't.