In startups that experience internet growth, you find yourself trying to build systems so fast and hire people that you aren't so worried about someone replacing the job you used to have because the nature of your job is changing as the company scales.
And if the startup is not growing, you can stop worrying about the equity package
By doing bad quality work on purpose will not make you learn anything. Better idea is to leave your underpaid position, start your own startup or join another that has better salary and compensation.