Market salary with stock upside plus the chance to level up a job title has potential to be a great deal
Titles obviously don’t transfer back to big companies, we had plenty of ex-cofounders and CTOs hired into the same junior roles as anyone else who could LeetCode.
Maybe you'd lose our on some tiny perk/benefit but that's not always the case.
So I'm not seeing what's wrong with this deal with the only caveat that the engineer has the experience not to overwork/burn out.
The startup can go bankrupt any moment, thats a big deal. You get crappy perks, often poor benefits.
At least with a startup you are going into it knowing that you have a higher probability of thing going south financially. With a big company, you might not get any warning at all.