I second this. I took a large salary cut to be 1/2 of an engineering team at a seed stage startup for ~1.25%. After 2 years of pretty grueling work I left to go back to big tech for 3x the pay. I wouldn't call it a total waste of time in the sense that it made me a better engineer, but it certainly wasn't worth it financially. The company still exists and has had a relatively successful series A and "A extension" but I don't think my equity will ever be worth anything.

I really wouldn't recommend anyone work as an engineer at an early stage startup unless you're getting ~5% or more (this would be unprecedented) because the risk is barely less than the founders and the pay is generally terrible. Series B or later (growth stage) may be a sweet spot where the salaries are decent and there is still significant equity upside without the insane hours.