If your battle plan basically hinges on the outcome of your initial alpha strike, and if a few dozen cruise missiles makes or breaks your alpha strike, you need a much better plan and much more hard power to make it workable.
The Chinese and PLA in particular have never been a fan of silver bullet plans because China’s long history has repeated hammered home the risks of that kind of strategy.
The job of SSNs have always been primarily about anti-shipping. VLS and land attack was only really added because of how overwhelmingly OP the USN sub fleet became towards the end of the Cold War and especially after, when the enemy essentially disappeared and they needed to justify their massive funding.
In no conflict that sub launched missiles have been used had those missiles made any decisive difference. Delete those subs and missiles from the equation and the result would have not changed at all.
For the PLAN to pursue, for all intents and purposes, a filler side quest when they are still some way from being able to confidently achieve the primary function of SSNs is very much putting the cart in front of the horse.
Its only when the PLAN sub fleet are confident in being able to effectively protect friendly surface fleets from enemy subs, and also being able to engage and hunt enemy subs on at least even footing that they should worry about land attack. Before that, such secondary missions are at best a needless distraction and at worst a massive misallocation of vital strategic resources.
I don't think you are appreciating how important that initial strike is. You can say we have so many missiles and victory is guaranteed. But realistically, there is always room for things not going right. If PLAN can find ways to increase its odds of quickly hitting USN/JSDF in the opening strike without putting itself in excessive danger, it should pursue that. If it finds the moves to be too risky, then obviously that would not make sense.
I think it is not incorrect to say that modern high intensity war between proper great powers is very sharp and violent in its opening stages, and while those opening stages may not wholesale determine the outcome of a war, it certainly can significantly influence the course in which subsequent phases occur.
In regards to the utility of SSNs carrying land attack weapons, the unique role that Tphuang describes is one where the SSNs offer a much wider geometry of attack against potential US targets in the Pacific. I.e. instead of ballistic missiles, cruise missiles coming from the Chinese mainland in a largely eastwards direction, they now must consider the serious threat of Chinese missiles coming from additional directions.
For land based air and missile defenses forcing the allocation of defenses to encompass all directions is not a minor thing, and would require the adversary to make significant additional investments to cover themselves from all angles.
However, for the PLAN at present and into this coming decade, I think it is also correct to say that one of the, if not the primary role of SSNs is still to conduct its regular subsurface activities and that would be much of the PLANs focus for their upcoming SSNs.
That is a reflection of how many SSNs they have and how capable they are, and what the threat environment is like.
Putting it another way, if the PLAN don't have enough SSNs and/or if they are insufficiently capable and/or if the threat environment at a given time is too unfavourable, then it would not be a good idea to have them launch strike missions with missiles, as that would expose them and put them at greater risk.
(However, it shouldn't be a matter of debate that SSNs have significant potential in augmenting the strike/missile role -- it just means we have to ask "when")
The more SSNs the PLAN has, the more capable they are, and the more favourable the underwater/ASW threat environment is at onset of hostilities, the more likely it would be that they will be okay allocating some SSNs to the strike/missile launch role at onset of hostilities.
So we should specifically be asking how likely it is that the PLAN would be okay doing it by the time they have 8 09IIIBs in service, IMO.