DACA was not yet challenged in court, unlike DAPA (I think that is the correct acronym). DAPA lost. DACA was about to be challenged in court.
It had to be rescinded because it was illegal.
I am not the one trying to play word games.
The only way this action becomes legal is to change the law. Not enforcing the law in such a broad manner has long been considered illegal. Such non enforcement decisions by the executive are valid only on a case by case basis.
BTW - if it were law, then Trump could not simply rescind it. Obama admitted this himself when he rightfully declared he did not have the authority back in 2014 or so.
Yet as you say, it was never challenged in court. So its legal status was never actually determined, was it? So therefore to claim that it was illegal is an opinion - which is fine - but nothing more.