I think the point you're missing is that "low performance" realtime applications exist and can often get by with more commodity hardware and careful software, eg. running a RTOS on x86 hardware. But that's usually not a viable option when your latency requirements are measured in clock cycles or nanoseconds rather than microseconds. For that, you need more specialized hardware that can do realtime and high performance.

"high-performance" could just as easily be interpreted as faster response time as compared to faster clock speed. So in that way they are "faster".

But real-time systems don’t guarantee faster. I was a real-time engineer for years.

Faster latency, not faster throughput.

Not necessarily even lower latency, just predictable.

In general usage, to perform means to do a job well, to fulfill the requirements well, right? But in computing in colloquial usage it's near universally used as a synonym for high execution speed.