That was precisely my point. “Show me the man and I’ll show you the crime” is the fact of how western legal systems work, the rule of law is a tale that they tell to impressionable schoolchildren.
Sure, when the state wants you, they'll get you. Read Three Felonies a Day: How the Feds Target the Innocent. I'm not one to say otherwise (quite the opposite), but for most people, most of the time, in most of their lives, western legal systems are pretty top notch in protecting people from arbitrary and corrupt application of the law.
In systems that truly embrace arbitrary and corrupt enforcement, it's quite a bit different system than largely objective traffic laws which society has agreed upon but which are rarely enforced (e.g. turn signals, lane merging in intersections, etc.) which turn into selective enforcement. I say this as someone who firmly believes that selective enforcement is ripe for abuse and has inherent problems, but on the balance I prefer the latitude I have as a driver in today's system than one where all traffic regs are enforced through automation at scale (which may be where we're headed in the next few decades, honestly). The reality is that as drivers, we probably curse the fact that these laws aren't enforced more often until we're the ones cited.
After all, when you refer definitionally to “the legal systems of the west”, to what alternative cohesive system of legal theory are you contrasting it to? There aren’t many, and they have differences we can measure. For example, those emphasizing divine revelation (Sharia) or subordination to the state interest (Chinese legal thought). Leave personal value judgements aside - it would be incorrect to think these systems operate the same way in practice or are “fundamentally the same”.
Outside of the few cohesive systems of theory and tradition that we can identify, the alternatives are systems characterized by capriciousness and corruption - the absence of the rule of law.
It's very true that both citizens' experience with their legal system changes drastically when state interests and national security are implicated. Like China, western legal systems recognize national security and public order as compelling state interests.
The difference is that an individual in China is far more likely to find themselves at an intersection of state and political interest with their individual activity (be it art, speech, action, association, religion, property) than one would find in the west. In China, the NSL structurally defines political security and cultural and social order as being within the national security framework. That's intentional and sits in contrast with the western tradition where the state generally needs to justify restrictions on protected individual conduct with a claim of state interest, and those claims are frequently subjected to an adversarial review process.
As you say, technology has already made surveillance far more intrusive and effective than anything available in the 20th century. Of course, the effect of the Stasi wasn't simply the surveillance, it was the uncertainty of never knowing if your colleagues, neighbors, or even family could be personally trusted - that environment of uncertainty was an intentional social control element. In a similar but not identical way, uncertainty is leveraged in the Chinese legal system: one may not necessarily know when their activity (or even past activities) have suddenly fallen on the wrong side of the national security line. This variability is not a bug in the system but a deliberate feature, and stands in contrast with the western legal systems.
Once entangled, there are bright line differences in the structure of those systems - opportunities to appeal are far fewer in China as a foundational difference, but opportunities to challenge the basis of the laws themselves and the justification for a claimed state interest essentially border on being non-existent. In contrast, individuals or classes of individuals bringing facial or as-applied challenges to overturn regulation or a claim of compelling state-interest is a frequent occurrence in US (for instance).
If we consider it a given that the state naturally seeks greater control of individuals (and I do), then the western legal system and particularly the US legal system, has been uniquely effective at constraining the state. In China, for example, it's not even a consideration that CCP leadership can be curtained through administrative proceedings.
But there's no arguing that in the US, if the stakes are high enough, they'll "get their man". On the flip side, the surveillance of the state itself by the citizens has also restricted the ability of the government to act with as much impunity as they did, say, sixty years ago. Specifically, policy body cams, ubiquitous cell phone video, one-party consent laws, legal clarity on recording public officials in public spaces, FOIA laws, etc. Nonetheless, it's disturbing and frustrating how inscrutable some very public events remain.
>"three felonies a day and the way China does it are fundamentally the same thing"
These are the statements that are incorrect for the reasons above.
Constraining the scope of those statements after the fact to narrowly apply to cases where individuals come to the particular attention of severe national security concerns in the respective countries allows for some "correctness" to the statement. But you have moved the goalpost if we are to read those comments so narrowly now - congrats! With appropriate qualifications your statements have become less wrong!
As mentioned, in contrast to the US, in China, social order and political security are scoped into the definition of national security - meaning that even if the mechanisms are the same, your ordinary Chinese citizen is far more constrained by the boundaries of the "national security" box than the US citizen. That an average citizen can successfully navigate the boundaries of their smaller box isn't the useful measurement when contrasting systems - all that fact does is convey that touching a hot stove gets you burnt and people learn from that. It does not change the fact that the Chinese legal system is fundamentally different than the western legal tradition in how it perceives rights and individual liberty and what recourse the average citizen has to challenge their encounters. This speaks directly to both of your claims at a high level.