Obamacare, not unlike health care in general, is very complex. There's lots of key provisions that one could use in that set of arguments.
Just one of them is the pre-existing coverage clause. Prior to Obamacare, an insurance company could deny you coverage for any pre-existing condition. This could be as mundane as taking ADD medicine.
That means nearly anyone cancould be told "no, you don't get insurance". And if one is making an OK living, they don't necessarily qualify for Medicaid.
So that's one of the big problems we had that was fixed with Obamacare. People that just couldn't get insurance, were then able to get it.
As for "treatment is never denied" that typically refers mainly to emergency rooms and even that is hardly universally true. Regardless, what an ER covers is merely a fraction of what health care needs people have and if it comes down to having to go to the ER, odds are the condition is too far gone in many cases.