I had a similar issue with OnePlus 7 but not at this scale. It lasted me for 3, 3.5 years. I think this is becoming a problem more increasingly because of a beefier and beefier hardware that is put into these phones, and the heat dissipation problem hence becomes larger and larger problem which doesn't get automagically solved. I think that the best bet today is to take one with "subpar" CPU and larger battery and not so crazy supercharging capabilities
Is this a new thing with newer OnePlus phones? We've had a OnePlus 7 and OnePlus 8 in our house for years and their batteries still work fine.