I wish it was a minor inconvenience for me, I have accidently given many business partners and vendors my personal cell which I did not want to do. Being in IT, people hold on to it forever or save it and I now show up as someone to add on social media apps. At least I can use the undo send feature of iMessage when that occurs.I also have the same issue with dual sim texts defaulting to the primary number. I went through settings, toggled iMessage off and on to see if that would help but nothing. Thought I changed something by mistake so for now I just switch off the primary line before sending a message via secondary. At least it is very infrequent that I have to send a message via secondary so it is just a minor inconvenience for now.
I'm going to remove my 2nd esim line from my phone and re-add but need to contact T-Mobile to do that since there's a QR code involved.