You could buy AGV/ASV using Amex Gyftr, and then recharge your google pay balance or buy a google play gift card and add it to your account and use that as a payment method. You need to add a debit card, but then you can set primary method as google play balance if it has enough balance in the...
One that i can think of immediately is that with charge cards you need to pay in full every month, no roll over. With regular CC with say, limit of 2L, txn would never go through, but with charge cards you can talk to amex and get a txn approved before carrying it out.