This doesn't have anything to do with latency really. It's about predictability. Given the system you described, there are so many edge cases that can potentially compound, that it is impossible to make any predictability guarantees about the system.
As an example, I worked on an embedded system that controlled electrical motors that was hard real time. The fast task time interval was once per millisecond. No matter what, that got called by the RTOS exactly 1000 times per second. When it didn't finish it's job in time, the result could easily wreck real world items or cause harm to people. Nobody even considered using interpreted languages in that project. The fast tasks all had provably run in much less than a millisecond. That means no loops that could be unbounded, no memory allocations, no recursion, no writing to flash, anything that was even slightly unpredictable was out.
So, even if you could prove that your system caused less accidents than a human driver when it was running well, it would be impossible to do an analysis that defined under what circumstances the system would be running well. Given that, it would not be allowed in a well-engineered real time or safety critical system.