Try basing an argument on the actual regulation rather than a prejudice on what you think it should be

Please find something in the regulation to support the assertion. A coupon is a componant of a ticket , it is not a ticket in its own right

The OP has 1 major element in his favour, the EU brought in these regulations to compensate passengers and to penalise airlines for downgrading and delaying/cancelling flights

If the passenger was rerouted in original cabin , with the advance notice , no compensation would be due. If a passenger is denied boarding then the compensation ex EU is a fixed amount up to EUR600 . For downgrading , the EU ruled that it is a percentage of the ticket price that counts

Arguing based on basis of EU regulations seems a lot more certain than arguments based on prejudices