Utter rubbish. I did this myself fairly recently in as much as I wiped my iPhone because it was painfully slow thereby deleting several eSIMs in the process. Having downloaded my details from Apple I contacted Three on another device and having passed security they emailed my eSIMs to me and I reinstalled them to my phone. Granted I needed to have my devices connected to WiFi but that was about it. So leave Three if you wish it’s entirely up to you.
