What this dissent basically says is "We should have ruled in favor of Trump, but we didn't". What is trying to be avoided, is certification that DACA was illegal in the first place. It's not just to protect Obama, it's to keep the door open for future EO's that violate the constitution in favor of immigration. They're treating it as if DACA was created through legislation, when it wasn't.
What this dissent basically says is "We should have ruled in favor of Trump, but we didn't". What is trying to be avoided, is certification that DACA was illegal in the first place. It's not just to protect Obama, it's to keep the door open for future EO's that violate the constitution in favor of immigration. They're treating it as if DACA was created through legislation, when it wasn't.