Look, it's very easy: UK licence holders had an EASA licence up and until the end of 2020. On 1 January 2021, their previously held EASA licence was retroactively removed and taken away from them. Do you call that fair?
It has absolutely nothing to do with Australia or Argentina. UK pilots were and continue to be trained to exactly the same Part-FCL requirements as the rest of EASA pilots. Most importantly, UK "WAS" EASA. Australia or Argentina have never been EASA countries. There is no precedent for an EASA Member State leaving and becoming a Third Country so no other case is comparable to this one.