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.
A few good early hires can be just as valuable as good founders.
Foinding engineers that need the job and would take it without any equity aren’t the difference-makers I’m talking about.
I'm glad you mention the pre-IPO mid-life startup and not solely trot out the usual "work for a FAANG instead and make $600k/yr out the gate" nonsense. There are quite a few pre-IPO mid-life (or even vaguely-but-not-super-early) startups out there that are doing well, growing more or less sustainably, will pay you a market-rate (or even above) base salary, and give you a solid equity package that has a much higher likelihood of being worth something than those early-stage startup options have. You might not make $600k/yr at a FAANG, but most people at a FAANG aren't making that, and many smart, talented people won't pass a FAANG interview anyway.
I quickly realized those are the absolute worst positions to be in. You take almost as much risk as the founders but almost none of the upside. One startup died, the other one sold for 100m$. Out of that I saw 400k$ as an exit. Not too bad but even with that exit I ended up making way less than if I joined a FAANG. In both cases the founders made millions (through the exit or through liquidity)
Now I'm a realist. Either you create/found a startup or it's not worth joining one as an employee. You have way more upside at a FAANG/pre-IPO mid-life startup that already found a great product market fit.
Essentially, founders are pushing a crazy narrative of Startups being worth it to early employees because they need them. It was sometimes fun but I wish I just joined a FAANG like most of my friends, I would have a couple millions by now if I did.