The term "差不多 (chabuduo)" could but is often NOT used with a shoulder shrug in day-to-day communication. The actual meaning, just like any other language, depends a lot on the context.
For questions asking for a mount of something ("How much ... would you like?"), it is common to answer that with 差不多兩匙 (about two spoons) or 差不多那樣 (that's about right). In this context it should translate to "about" or "about right".
When someone is being annoying, people in the northern part of China would often say 差不多得了, which means "that's enough, stop it".
Of course, there would be mediocre people use this phrase with a shoulder shrug. The problem is the attitude, which as you said, is not culturally specific to Chinese.
> It's an attitude very prevalent in Mainland China
Mainland China has a huge population. Even if just 10% of them having this attitude, that is still a lot of people. There is a good chance you have met some of them, as I did myself, unfortunately.
There is also bias. Cheap products, regardless where it is made, has a higher probability to fall apart after a few months. You will only hear it from the news if a building collapsed or there was a terrible incident; if everything works -- as it should -- it won't make the headlines.
There is also a term for poorly-built projects, 豆腐渣工程（ https://en.wikipedia.org/wiki/Tofu-dreg_project) and people are furious when they read about it. People cut corners because they have the incentive to do so and they know they might be able to get way with it by paying a relatively small penalty to the potential gain.
It is not a "chabuduo", it is actually about taking a precisely calculated risk. The flawed system is giving the people the wrong incentive, that's what holding China back from its full potential.
> I haven't encountered this in Taiwan, Malaysia, Singapore, or even Hong Kong.
That's probably just because you haven't stayed in those place long enough. A quick search in Spotify gives you:
* 差不多姑娘 by G.E.M, a singer in Hong Kong: https://open.spotify.com/album/28sxY4WxuFLQ5wMeugtyAp
* 差不多先生 by MC HotDog, from Taiwan: https://open.spotify.com/album/7xEo9EqHb4X52fA7DGiDPg
* and so on...