If you use the smartphone/ tablet as cold storage, I dont see an issue if it will by mistake connect to the internet at some point. Yes it is not the best that can happen, but it will not automatically download a bitcoin specific virus, that cracks your encrypted wallet in no time. Seems a little bit to paranoid to me.
I agree with you but if you are storing several Bitcoins into your device, you want to avoid the risk that a malware could be waiting somewhere in your OS and will be able to send your seed to someone once your device will be connected to internet, even briefly. The topic is about replacing a hardware wallet by an old smartphone, you can't accept any flaw.