Is that within federal government's power?- House and Senate to basically we basically can't sort the mess left behind one bill so just let the State government put in legislation to fix it up. Could they for instance have done it for the Affordable Care Act?
They could have, but it wasn't a particularly popular solution. It left in place most of the Obamacare taxes and the Obamacare spending.
That's the real problem. The states don't want to pass their own healthcare plans, as they want the federal government to pay for it. Under Obamacare, the federal government pays for 90% of the Medicaid expansion and 100% of the premium subsidies. If it weren't for that, the federal government could have passed a clean repeal. The states would then, without federal interference, be able to pass their own plans if they wanted to do so.
A clean repeal would not have interfered with federal supremacy. It simply would have returned things to the old status quo. Even the Collins/Cassidy plan wouldn't have impacted federal supremacy. It just offered an option for how the states complied with federal law.
There are also many laws that expressly do not pre-empt state law on the same subject (e.g. the Fair Debt Collection Practices Act).
There are a few that vest court jurisdiction to enforce a federal law exclusively in state courts (e.g. the Junk Fax law).
And, there are federal laws and court doctrines that incorporate local state law when applying state law (e.g. bankruptcy exemptions from creditors at 11 U.S.C. § 522(2), a variety of state substantive law principles under the Erie doctrine, the Assimilative Crimes Act applicable in federal territories).
Is it theoretically possible? Sure. The federal government can generally pass whatever laws it wants (obviously must me constitutionally abiding). Therefore it can pass a law that structures the federal healthcare system in such a way that states can override chunks of it over time.
How would this work? What would the details be? Would it even be realistic in the current political environment? That is very complicated and well beyond the scope of this answer.