According to the website, Diners has about more than 1000 lounges, while PP has about more than 1300. Typically most of them overlap. But there are certain lounges that have access through Diners where PP is not accepted. They are very few in number, it wouldn't make much of a difference. For eg, in KUL, PP has Travelers B&G and Sphere Lounge. But Diners has three- You can access Sama Sama Express (Can also be accessed through Amex plat too) too. But then, if you have an Amex Plat, you have access to Plaza Premium lounges in addition to Sama Sama Express. PP had broken ties with Plaza Premium in July 2021 (even though they have regional tie-ups in certain places such as Delhi for eg.)