Unfortunately if the CPU is waiting for memory, then thread is stuck, even if the hardware CPU had resources to execute some other instructions it cannot execut

Unfortunately if the CPU is waiting for memory, then thread is stuck, even if the hardware CPU had resources to execute some other instructions it cannot execute them from the same stream of instructions. Instead it could execute another stream of instructions, i.e. another thread. This is how hyperthreading works and still requires you to write a multithreaded application with the same problems and requirements.