Washington state law certainly does apply. The state did not sign a mandatory binding arbitration agreement. The employee/contractor may not have the right to bring suit against Instacart, but the state maintains that right.
Thought experiment: could Instacart assault, kidnap, or murder a delivery driver and claim that arbitration is the only venue for redress?
And even then, the worker does have the right to petition the court to review the clause itself. So the worker can still sue with the knowledge that it will be thrown out if the judge decides to uphold the arbitration clause.
Thought experiment: could Instacart assault, kidnap, or murder a delivery driver and claim that arbitration is the only venue for redress?