Can you say for sure that it wasn't like that out of the box? It wouldn't have gotten worse, you should have been able to tell right away when you first opened the lid.
By looking at this picture that lid had to be pushed well past 90 degrees to cause the deflection between lobes of the lid...
It would take a lot of torsion to do that kind of damage. Standard usage in an upright position would make it very difficult to generate enough force to do that without the cooler tipping back and over. One way I could see this happen is if the cooler is turned upside down with the lid open...
Take a look at the Grizzly Drifter Soft Sided coolers. The liner is super strong TPU, with the roll top you'll have two layers of leak protection.
Use code RD10 to get the 10% Off River Dave's discount.
This WAS a 100% Grizzly design. Unfortunately a dishonest factory owner in China showed an agent the product and the unfinished cooler was knowingly stolen and released for "sale" by another company.
https://www.instagram.com/p/8MIjMvOZcN/