Even if unions are affecting no change, their are able to give the workers at least some power.

Who knows, maybe they'll make Amazon to allow unmetered bathroom breaks one day.

Bathroom breaks aren't metered in Amazon warehouses.

Besides using your own break time to go, they are absolutely metered for many direct roles in the exact sense that using the restroom can decrease your speed performance metrics which can lead to progressive coaching or other negative consequences.

It literally is considered time off task (TOT) when you stop for a restroom break outside of your scheduled break times.

There is always the option for people with increased medical restroom needs to seek specific accommodations to essentially excuse the TOT for their needs.

Maybe there’s a confusion of terms here, because I think everything you’re saying is what it means for a bathroom break to be unmetered. You can go to the restroom whenever you’d like, as long as you’re getting the work done. If you had specific declared bathroom breaks where the company keeps count and pauses performance metrics for the duration, that’s what I’d call metered breaks.

They’ve been getting injured at a higher rate since Amazon introduced robots to the warehouses and Amazon tries to limit their access to healthcare to avoid workers comp claims. This is definitely something a union would address.