the problem is that low latency is not absolutely defined, and it's a bit of a buzzword so people who don't know about the specific niches just don't get why java won't cut and you need c++ rust or similar to meet targets there.
That's it. That's what an RT system is. I don't care if your latency is 1us, 1ms, 1s or 1h. If you can't miss the deadline then your system is a real-time one.
Low-latency then depend on how your strategy works and your particular needs. It's useless to have sub ms timing of stock market data if your results take seconds to calculate.
Of course, your strategy that takes 1s might be more lucrative than one that takes 10ms to calculate. Then it's up to you and your algos.
Decoding video and interactive rendering is a great example of an RT system. If you can't construct a frame within (usually) 16 ms you skip it and start with the next one.
It's a good example of a problem where a realtime system would be useful but it's not a good example of a real-life realtime application (usually).
I have never understood why people might think it ought to be faster.
The time to market argument is really stupid imo.