You don't get a sign-on bonus every year either. Agreed, I'd say at most you're getting $250k/year in equity, no way L6 is getting $3.2M in equity over 4 years

The sign-on bonuses are amortized over the equity vest period (which is a bizarre way to do it, but whatever). Aggressive L4 offers can clear about $250k/year in equity, so I don't know where you're getting this "at most" quantity...

Research scientist ladder at Google is a higher comp band than swe by, at least for lower levels, about 1 level. So an L6 RS getting high l7 swe comp isn't out of the question.

That said, the person getting such a large stock grant with a lower base salary is suspicious. The other two offers for L6 are clearly correct as they are (160K/year stock is too low for L6), but that one is odd. Doesn't mean it's wrong though.

For some context, initial grants are usually larger than refresh grants, and an L6 SWE (who again is in a lower band than L6 RS) can expect a >200K stock refresh. So a new hire RS at that level isn't going to get less than 200K annually (or 800K/4yr).