In a helpful comment on this Android Stackexchange question, prominent contributor alecxs states:
google and OEMs will always have own backdoors in propritary [sic] blobs for baseband/modem etc - you are already hacked at moment of using smartphone
I have much respect for alecxs, and they have provided helpful answers to my questions in the past. So when alecxs writes something I don't already know, I pay close attention and try to learn form it.
Is it accurate that Google and OEMs always have backdoors in Android, and therefore one should consider any Android smartphone to be already hacked?
If so, why does the baseband/modem require such a backdoor?