Not sure how you arrived at 60% - aren't federal capital gains topped off at 20%, and this bill only 7% for gains over $250,000?

Even if it is 60%, I think that's reasonable. In your case, why is the employee selling all of their stock in one year? If they sell over multiple years, they could get gains of up to $250,000 without paying any state tax, which is plenty.

I'd also be in favor of a state income tax, since the sales tax regime in Washington is very regressive.