That’s true with any electric heater element. It’s called pulse width modulation (PWM) and is actually very effective when done properly. Seems like the frequency is too long on yours. It should be cycling many times per second, meaning the full power is only on for milliseconds at a time, nowhere near enough to actually burn things.
Even a cheap Arduino is capable of PWM at 16MHz (16 million duty cycles per second; we’re talking microseconds here now). So I’d think even a cheap one should have good PWM control, but I guess you get what you pay for.