Where exactly are developers reporting six-figure signing bonuses? Google, Amazon, FB, etc I assume?
Also, making $150k with a $150k signing bonus is not anywhere close to 'making $300k'. What do you earn in year 2? $150k (plus whatever raise and annual bonus, but annual bonuses don't typically make up a huge part of your annual income in software, as they do in finance).
Almost the same in cash, but a little more in stock grants.
Years 3 and 4 have a lower salary but much larger stock grant vesting, that at today's stock price mean that I'd be making roughly the same amount in each year. If their stock crashes, then I might leave, though they mentioned that after the second year they may up the stock grants for the following years.
And if their stock keeps going up (as it has been), then I would be getting a de facto raise in years 3-4. But I'm fine with the first 2 years; my personal burn rate is low, and it would let me work on personal projects full time again after the two years are up.
Also, making $150k with a $150k signing bonus is not anywhere close to 'making $300k'. What do you earn in year 2? $150k (plus whatever raise and annual bonus, but annual bonuses don't typically make up a huge part of your annual income in software, as they do in finance).