Commonwealth law is supreme to state law FWICS; there is no utter sovereignty of states, or else the commonwealth government would not exist and each state would have its own governor general. Also, Part V, section 51vi outlines the powers that the Parliament has to enforce Commonwealth law(s).
Has Morrison ever spoken out against the draconian state lockdowns? I don’t recall any time he did.
No, it isn't.
I've actually studied Australia's constitutional law. I understand you've no particular reason to understand it, but I have to.
there is no utter sovereignty of states, or else the commonwealth government would not exist and each state would have its own governor general.
States have control over all areas where there is no 'head of power' outlined in the Constitution. The Commonwealth only has power over areas where the Constitution gives it a 'head of power'.
Each state does have its own Governor, appointed by the Queen on the advice of the Premier of that state, in exactly the same way that the Governor General is appointed by the Queen on the advice of the Prime Minister of Australia. The Governor General does not outrank the state Governors except in matters of protocol and ceremony.
The clearest way to explain this is to look at the difference between Canada and Australia - Canada's provinces have Lieutenant Governors, not Governors, and they are appointed by the Governor General of Canada, not by the Queen. Whereas, as I've just said, Australian states have their own Governors directly appointed by the Queen.
The Commonwealth government does not outrank the state governments - it just has responsibilities for different areas.
You've obviously looked at Section 51, because you've mentioned part of it (although Section vi doesn't work the way you seem to think it does - it allows the Commonwealth to use its resources to enforce Commonwealth law, yes, but only in cases where Commonwealth law applies - it can't overrule state laws in cases where the states have jurisdiction). That's the relevant section in the Constitution here - you'll notice they are 39 areas (i to xxxix) - there are the 'heads of power' I referred to earlier. They are the areas where the Commonwealth has jurisdiction. The Commonwealth has no jurisdiction over any area not specifically mentioned in those 39 categories. Go through them - you'll notice that health isn't clearly included. So state governments have control over public health.
Section xxiii(a) (which was added by an amendment in 1946 - amending the constitution requires a referendum in which a majority of the Australian population overall votes yes, and a majority of the population in a majority of states votes yes - it's difficult to amend the Australian constitution) gives the Commonwealth control over some health funding for welfare purpose - but no control over actual health law. Every state sets its own laws on public health matters and the Commonwealth cannot overrule them. Section vi gives the Commonwealth control over quarantine, but the High Court has ruled that only applies to quarantining people coming from outside Australia - not within Australia - again, the decision to quarantine those matters is in the hands of the states not the Commonwealth government. This is how Australia's constitution works. All decisions on lockdowns have been taken by state governments.
Has Morrison ever spoken out against the draconian state lockdowns? I don’t recall any time he did.
Yes, he has - repeatedly and often. This has actually been one of the major features of Australian political news over the last year. Morrison trying to stop states from constantly and repeatedly locking down and them just ignoring him because they are the ones with the power - most particularly his brawls with the Premier of the most lockdowned state, Victoria (where I live), Daniel Andrews. If this isn't getting any news coverage outside Australia, then hell, that's bloody disturbing.
I'll just give you a few links grabbed from google news.
For the others, I'll just share links, but I want to briefly include an extract from this one which is almost exactly a year old now. I've underlined the most important part.
Victorian Premier Daniel Andrews is under growing pressure to solve the state's coronavirus crisis quicker than he has proposed in his roadmap out of lockdown. Prime Minister Scott Morrison and his senior ministers are holding a blowtorch to the premier, saying his plan is doomed to fail and urging him to listen to the frustration of millions living in the nation's strictest lockdown.
Mr Morrison began a day of intense criticisms aimed at Mr Andrews by comparing his plan unfavourably to the New South Wales "gold standard" of contact tracing at the core of fighting COVID-19.
He said Mr Andrews' roadmap, revealed on Sunday, was "crushing news" and he hoped it was a worst-case scenario for the state.
But "we do not have that authority to step in and tell the Victorian government they have to follow another plan. That is not how Australia's federation works," Mr Morrison said.
For the others, I'll just include some links.
Morrison takes aim at Victoria's lockdown, warning of 'very severe' impact on national economy
Lockdowns ‘need to end’ in Australia: Morrison
'We can't stay in the cave': PM hits back at state opposition to COVID-normal
Lockdowns signal virus failure, says Scott Morrison
Morrison hasn't opposed every single lockdown - he's supported some short ones during the worst outbreaks. In recent weeks, he's been a bit more supportive of the idea, but that's mostly because he's negotiating with the states to try and limit how often they will happen, and to do that, he's had to dial back his hostility or they just won't listen at all. But, yes, Morrison has been consistent throughout this entire pandemic in opposing nearly all severe lockdowns. If it was his decision, we wouldn't have had anywhere near as many.
All lockdowns have been the decisions of state governments - that's why Victoria (lead by socialist Dan Andrews who is utterly paranoid) has been in lockdown for over 200 days over the last year and looks like we're going to be in lockdown until nearly Christmas at the moment, while NSW (lead by conservative Gladys Berejiklian who has done her best to limit lockdowns up until NSW has wound up with the worst COVID figures in the country) only went into a serious lockdown for the first time recently and is planning on trying to come mostly out of it next month. It's state government decisions - not Federal and the Federal government cannot overrule them constitutionally.