The problem is not that it "prompts" you to use the new AI generated one, it is that it is now DEFAULTING to the AI generated one, and forcing you to manually choose to use your defined default message and subject.

And worse?  If you click on an arrow next to invoice from the invoices screen and choose "Send" it sends the invoice with the AI Generated subject and message with no input from you at all, completely ignoring your specified defaults.  This is unacceptable.  AI generated content should always be opt-in, not 10 extra clicks opt-out every single time.  What is the point of us defining our preferred default subject line and messages if you're just going to ignore it?