I think it's always gonna be a balance between maintaining an optimal level of secrecy for security reasons and selling up the deterrence value/marketability of one's gear. Exactly where to put the pivot point is dependent on various factors, like the country's military capabilities relative to potential rivals and the country's geopolitical relationships.
For technologically backward countries like North Korea, their gear is vastly outdated and outclassed so they sell it way up while being very secretive. This means that while enemies will have a tough time figuring out exactly how capable they are, and the big upsell means that enemies will possibly assume they are more advanced than they are and be deterred from attacking them while domestic citizens are reassured of the country's strength.
For advanced countries like the US, their gear is the best so it makes sense to show off openly what they have, because they are not afraid of revealing possible deficiencies others can take advantage of when it comes to gear. Likewise, this works in favour of their military deterrence as well as their export attractiveness.
Just think about the evolution of China's foreign strategy over the years:
Mao Years: Antagonistic relationship with world powers, materially backwards, thus highly secretive yet gung-ho attitude (like North Korea).
Deng Years: Warm relationship with world powers but harboring private ambitions, materially backwards, thus less secretive and a reserved, quiet attitude (Deng's 'Hide and Bide' strategy).
China Now: Competitive relationship with world powers, materially catching up, thus...
China is more advanced now but still lags behind the West in terms of gear and capabilities. Like before, it doesn't want the West to know just how advanced it is (just how much it lags behind), but with tensions bubbling over a number of flashpoints where it is pushing against the US dominant regional security order, it also needs to show itself as possessing a credible military deterrence. This is a partial departure from the Deng strategy you seem to promote. This is also why over the last 10 or so years, we have seen complementary rises in China's geopolitical assertiveness as well as the quality of its gear and the publicity around said gear.
I do not believe the publicity and portrayal by state media of their equipment has increased in any major way over the last ten years -- the degree of relative publicity has remained the same, it is just that they have improved their capability so much that the same degree of publicity makes it
I also do not believe that the state media's portrayal of the military fulfills your original quote of trying to "perception that Chinese military industry is more advanced than it is" or that they are trying to create the perception that the Chinese military is more capable than it is.
I remain suspect of such clean divisions between what you see as "having high levels of capability" and "striving for improvements in capability." I think this division is contrived and that the reality is far more ambiguous. Getting down to brass tacks, the Chinese state media makes PR about its military and military gear. Being PR, it does not present a fully objective picture of the real state of affairs, i.e. the PR content, usually being vague, is always optimistic in its conclusions. Now does an optimistic bias on Chinese military capabilities not benefit the interests of the Chinese state? Short of revealing sensitive information, I think it certainly does.
I acknowledge that there is not a clean division between "having high levels of capability" and "striving for improvements in capability".
I would also agree that the portrayal of the military is generally to portray it in an optimistic way, or at least to portray the military's development in a broadly positive way.
BUT, I hope you realize why "portraying the military in an optimistic way" is quite different to what you originally claimed i.e.: creating the "perception that Chinese military industry is more advanced than it is" or creating the perception that the Chinese military is more capable than it is.
To portray one's military in an optimistic way does not mean one has to reveal the true advancement of one's military industry nor does it mean one has to reveal the true extent of one's capability -- and it definitely doesn't mean one needs to exaggerate their level of advancement or exaggerate their true capability.
Given we are all experienced PLA watchers here, we imagine we are all acutely aware of just how little we know about the most advanced capabilities and assets that they deploy which we have little to no information about which any normal western military or even military in Russia or India would have openly disclosed. I'm not even talking about WMDs or strategic weapons like ballistic missiles, but simply conventional weapons (like fighters, ships, AEW&C, AFVs, even small arms!) and basic information about their development, testing, fielding statuses.
So that is why I am saying Chinese state media is doing the complete opposite of what you're saying -- overall, they are deliberately creating the perception that the Chinese military industry is less advanced than it is, and creating the perception that the Chinese military is less capable than it is. And they are doing that by withholding information about the status of a variety of weapons, technologies and even basic information like order of battle, and even often not organically acknowledging the existence of a new weapon until it has been deployed.
That is why I find the idea that the Chinese state media are seeking to create the "perception that Chinese military industry is more advanced than it is" or create the perception that the Chinese military is more capable than it is to be absolutely preposterous.
I will fully agree that Chinese state media generally seeks to create a positive portrayal or depiction of the military and their progress -- and that positive depiction of course does benefit China as a state as it allows them to conduct PR and news outreach to the public, resulting in a positive public confidence to the military, especially by the vast majority of the public who are very unaware of just how little information and how little true capability the state media depictions actually reveal.
BUT state media most definitely are not trying to create any sort of exaggerated or even accurate depiction of the state of the domestic military industry or the military's actual level of capability, and in fact they are doing the complete opposite.
edit:
I think the biggest problem I have with your original statement is this part (bolded): trying to "perception that Chinese military industry is
more advanced
than it is," or that they are trying to create the perception that the Chinese military is
more capable
than it is.
Because saying "more XYZ than it is" means that their depiction of either military industry or military capability is an exaggerated portrayal of the reality. As I've repeatedly demonstrated above, we obviously all know that this isn't true because the Chinese military actively withholds a variety of very basic information about their deployed weapons and have very high opsec for weapons under development, to such a high degree which is quite different to other equivalent weapons of foreign military forces.
If you said that they are trying to create "the perception that Chinese military industry is advanced" then I would partly agree with you. Or even more accurate if you said that they are trying to create "the perception that Chinese military industry is advanced without revealing just how advanced they really are" then I would fully agree with that statement.
(and same goes for Chinese military capability too -- i.e.: creating the perception that the Chinese military is capable without revealing just how capable they really are)
Sure why not