I can understand the frustration caused by the choices of the UK government. And of course it is a course of action to petition said government to change its mind.
However, there is of course another party to any such agreement, and the situation has now changed. There is a huge surplus of pilots in the EU to begin with, without having to accommodate third country immigrant workers competing for jobs and driving down wages even more than they are now already. In the end, the EU is responsible for the wellbeing of its own citizens, not those of third countries. Therefore, there is of course a justified case to be made to make it easier for EU citizens to reclaim their EASA license, not so much for non-EU citizens.
The EU never demanded license acceptance by the UK, it was the unilateral choice of the UK to grant that, most probably driven by the inability to exchange former UK issued EASA licenses to valid UK licenses in a timely manner and under lobbying from UK airlines, who, unlike their employees, sometimes do get heard at government level.