If it's lopsided, on average it's lopsided in the opposite direction: companies have massively more leverage than the average employee, and the damage to employees for no-justification layoffs is much larger, on average, than the damage to employers for no-justification resignations. Think of it from Google's perspective: if someone turns down a Google offer, even at the last minute, Google hardly cares. But if Google rescinds an offer at the last minute, it is a pretty big deal for the opposite party.

Between a startup and a prospective employee, things are more on a level of parity.