Is there a way to set up a price list to be universal for all customers, without having to add the customer to the specific Price List/Discount List group on the customer record?
You can apply price lists to Customer Groups.
If you did not create customer groups, you can use DMT to apply a group to your existing customers.
You can also create a Post Processing Method Directive on GetNewCustomer to default the customer group for any new customer. This is what we did for this exact reason.