Feels like there should be the equivalent of Matt Levine's "Certificate of Dumb Investment" for this scenario. ~90% of startups fail. Your equity is statistically likely to be worth $0. You will likely grind for years with nothing to show for it except the experience, your network, and whatever cash comp you collected. Proceed accordingly.

https://news.ycombinator.com/item?id=24285305

(edit: totally fine to still jump into a startup role if you're not optimizing for quality of life and economics; I did because I enjoyed the work and the team)