"realistically" .. I don't think it's much to ask a Belgian bank (or offering accounts in Belgium) to actually support Belgian customers?

Unless they let go of every single customer with diacritics in their name, the complaint would still stand. Especially since the case is brought by a government body, not the end-customer.

The "throw your hands in the air" move for the bank wouldn't be to ditch this single customer, it'd be to ditch the entire eurozone. Remediation is likely cheaper.