Something else must have been wrong, because that's not the way QoS works IIUC. MVNO subscriber equipment receives the same signal strength as the carrier's own subscribers do, but packets are deprioritized, resulting in occasionally slower service with higher latency. But battery draining isn't supposed to result.

There are a few big MVNOs (like Straight Talk) that work across multiple carriers - I bet in the face of deprioritization the phone tried to switch to another network, and kept doing that as the new carrier also experienced congestion.

It's not a real time switching but you've an option to pickup the network and change to a new network if you want .Like it's either or

Oh, interesting! My Pixel 7 seems to run out of battery really fast too (vs previous Pixels, which I've had many of). I first thought it was 5G, but LTE doesn't seem much better. Now that I think about it, I switched to Fi at around the same time... wonder if it's actually that causing the drain?

Google Fi seems to prioritize T-Mobile networks in my experience, maybe monetary related, but they had terrible signal near me. I got an app on the play store to force it to US cell, but I constantly had to switch it. I wouldn't trust the Google Fi app to "automatically choose the best network" _for you_.