RuPay-Discover/Diners club card is not accepted on many places outside India including International lounge access.
However, RuPay-JCB cards accepted almost everywhere outside India.
Last week, i read this news Discover global card's alliance transaction market share decrease including RuPay and Diners club card.
The reason was not mentioned in the news but I believe that 50% places dnt accept Discover global card network that's why transaction market share decrease.
Last month, I also read the news that Discover's market share has gone down by 25%, there was talk that some other companies/bank may acquire Discover Bank and Diners Club Card.