NodeJS is intended for IO-heavy workloads. Specifically, it's intended for workloads that don't benefit from parallel processing in the CPU.
This is because Javascript is strictly a single-threaded language; IE, it doesn't support shared access to memory from multiple threads. (And this is because Javascript was written for controlling a UI, and historically UI is all handled on a single thread.)
If you need true multithreading, there are plenty of languages that support it. Either you picked the wrong language, or you might want to consider creating a library in another language and calling into it from NodeJS.
I didn't say multithreading anywhere. Mutitasking (concurrency) != Multithreading.
You can do pre-emptive concurrency with a single thread in other runtimes, where each task gets a pre-defined amount of CPU time slice, that solves fair scheduling for both IO and CPU-bound workloads. Nobody is supposed to pick NodeJS for CPU-bound workload, but you cannot escape JSON parse/stringify event-loop blocking in practice (which is CPU-bound).
NodeJS is intended for IO-heavy workloads. Specifically, it's intended for workloads that don't benefit from parallel processing in the CPU.
This is because Javascript is strictly a single-threaded language; IE, it doesn't support shared access to memory from multiple threads. (And this is because Javascript was written for controlling a UI, and historically UI is all handled on a single thread.)
If you need true multithreading, there are plenty of languages that support it. Either you picked the wrong language, or you might want to consider creating a library in another language and calling into it from NodeJS.