Your point that a party to a contract could waive their contractual rights is true but I would also argue that you are also choosing words to frame the narrative when you say the Uber "forced the contractor" rather than saying that Uber exercised its contractual rights to resolve the dispute via arbitration. In fact isn't the contractor who is trying to "force" Uber to give up its contractual rights by claiming that the contractual terms aren't valid? [edit: corrected are to aren't]
There is a larger discussion about the value/fairness of arbitration as a mechanism but as I understand it, it is established law that arbitration clauses are legal and I don't think anyone is arguing that Uber has "forced" someone to enter into the driver's contract with Uber.