It shouldn't depend on the payment processor; if the credit card payment is going to Patreon, they can batch up the charges however they way (e.g. they could batch up all of one customer's donations for a week to 50 different artists, and process a single transaction with their payment processor for the whole amount. They would then only be charged for a single transaction)
Even if it was 1:1, actually charging the payment processing fee for the payment processed would be fine. The person with one pledge for $1 to one creator would be charged $1.38. The person with one pledge for $100 to one creator would be charged $103.80. The person with 100 pledges for $1 to 100 creators would be charged $103.80. Fine. With the rules they're putting into place, the person with 100 pledges for $1 to 100 creators will be charged $138.00 - with the other $37 going to Patreon. Not cool.
