For some things you can opt out of arbitration, but not for others.
The online fi related contract (which I obviously not the actual carrier contract) I found is: https://fi.google.com/about/device-protection-terms/ which indeed has a mandatory arbitration clause.
It's high time that the arbitration act gets dramatically scaled back. I don't have problems with reasonably sized companies agreeing to arbitration in contracts with each other, but it doesn't work for end users and employees.
However, given that it takes years for any case to settle, if you could even find how to start the process in the first place, that ain't happening.
I am former Fi user, started back when it was a "Project". My Nexus 5X's battery swelled but was still working and had a full charge, they wanted me to ship it back to them which I morally felt I couldn't do, and replace it with a generally low quality Lenovo Motorola phone that was reported to have serious WiFi problems, negating that major part of their business proposition where it uses any accessible WiFi for data and voice if possible. Felt stupid for having paid them $5/month for device replacement coverage.
The G+ real names debacle prompted me to remove as much exposure to Google as possible, now I'm down to Google Groups which can only be had from them. They're just too risky for individuals to depend on.