If your MX is 2016, I think your battery is actually covered for 8 years and unlimited miles. But just a month or 2 ago, they changed it 125,000 miles. I don't know what happened if you try to tell them the original warranty is for unlimited miles. And since you are in California you will get at least 125,000 miles... I think it was a CA law to cover at least 125,000 miles for hybrid battery and EV battery.
It's good that your MX had very little problem. Our 2017 MX had a few door problems already in the 2 years we had it. Unlike the S or 3, the X got auto doors everywhere. It is very common for some of the sensors and actuators to fail. And MCU1 will probably fail in under 6 years. That alone is like $3000 to replace I think. Our FWDs works perfectly so far, but it seems like it is something that could fail easily with so many moving parts and sensors. So I bought the extended warranty.