While I don't like VC math and we (I'm CEO and co-founder) at Aryn AI give more than 1% for founding engineers, numbers like 5% to 25% are really a reflection of the risk and not the work. Prior to an equity round, you can give that away and you're treating the founding engineers like minor founders. Post an equity round, there isn't enough left to give everyone that and still build a decent team.
After an equity round with decent funding for 2-3 years, the co-founders have convinced someone to part with lots of money with no guarantee of an exit. There are innumerable YC startups and well-known VC-backed companies that have been sold for parts. After an equity round, you are joining a startup with some runway that you would not have gotten on your own, and hopefully, working on an opportunity that is outsized. Otherwise, you shouldn't take it.
Outsized means that even if the founders are gazillionaires, you may be 1/20 of a gazillionaire, which is still a gazillionaire. Otherwise, it would have been better for everyone to have worked for some big tech firm anyways. It really is a zero to one game, and you don't get to do it often. So do it if its compelling and fun and the outsized reward is and has always been a lottery ticket.