First, for startups which take VC, a "modest exit" can mean that the founders get nothing. The range of outcomes where founders become fabulously wealthy but early employees do not is fairly narrow.
Second, most founders start off by not taking a salary. Deciding to be an employee instead of founding your own startup means implicitly deciding to take more salary up-front and less of a chance of holding valuable stock at the end -- put another way, reducing your risk.
That all said, whether "a fraction of a percent" equity is reasonable is an open question -- it depends on how large the company already is, how large your salary is, et cetera. You can always negotiate.