Hang on. City level officials play an incredibly important role in China. While Nanjing is not in the same tier as Shanghai, Beijing, or Shenzhen, it is in the tier just below them. It is the provincial capital of one of China's most important provinces -- GDP similar to Texas. Many large Chinese companies are often tied to specific cities -- they get grants and subsidies via the city they are located in.

This guy did it over 30 years so it is feasible.

Scapegoat isn't the right term but I think it is very possible he is being executed to essentially send a message. I think your bigger point that there are way more corrupt officials than just this guy involved seems very plausible.

It's not outside the realm of possibility for the positions he occupied. But yes, corruption is selectively cracked down upon in China

That's not how this works. It really depends on how close you are to a position, where people might want to bribe you. Low provincial officials with direct ties to local land development might e.g. be able to take many more bribes than a highly ranked official in an office that is far removed from economic activity.

Over thirty years? I am surprised he didn't take more.

Nah he took the bribes and probably paid 90% upward/laterally. Being the guy that actually takes the bribe is likely part of how he got promoted to where he is, in a way, like a soldier who gets promoted for being a calculated risk taker.