Visa/mastercard charged conversion rates because Visa/mastercard was launched to help America and American dollars will get stronger.
Visa/mastercard first conversion our Indian currency to US dollar and then paid to international merchants.
Now how RuPay card works ?
When we use RuPay card, we paid in INR currency,
Other countries central bank/local banks opened bank account in India. Now when we use RuPay card on any foreign countries, RuPay card deposits INR currency in the bank account of that country's bank and foreign banks deposit same amount of foreign currency to the merchant.
This thing also work vice versa. JCB card also use local Japanese currency and also trade with INR-Japanese yen.
One person told me he used Canara bank RuPay credit card in Spain. He didn't pay any extra international conversion currency rates.
The more we use Visa/Mastercard, the more we lose INR currency and US dollar gets stronger but the more we use RuPay card/UPI, our Indian Rupee will get stronger because eventually all countries will use INR currency to do business/trade with India.
last thing, MasterCard charges higher MDR fees compare with Visa card.so, if you dnt want to use RuPay card then use atleast Visa card.
