the solution to untrustworthy devices on your network is to use more trustworthy devices
This kind of "oh, only buy perfect end devices" is just as worthless advice as "oh, only buy service from perfect ISPs that don't make you want to encrypt traffic."
It doesn't have to be perfect. It should, however, not actively work against its owner, and the manufacturer should provide enough information and access that the device's owner can be reasonably confident that the device is acting in their interests.
This kind of "oh, only buy perfect end devices" is just as worthless advice as "oh, only buy service from perfect ISPs that don't make you want to encrypt traffic."