only there is no process isolation so no strong guarantee that secrets aren't leaked. no control over baseband makes the whole environment in which (other privacy protecting) apps are running extremely hostile from a security pov.
Modern Android/Qualcomm phones have pretty sophisticated security architectures that do indeed isolate the baseband, partly because exploiting baseband bugs was such a common source of phone unlocks in the past. If an app is using SSL then the baseband can't read what's happening.
