I got told recently by a friend essentially that as long as you're paid, does it matter? They'll pay you to fix it too....
If they won't listen at all, I'd voice/get your opinion noted for the record, then fix it after they get their way and it doesn't quite work out.
It's a really hard battle to have. Unless you can find an equivalent version based on what they do, so they can see that it's just the tip of the iceberg and would say the same to you, there isn't a lot of winning in these conversations.
The other option is you get the chat sent to you, you ask more detailed, specific q's to get the "tech detail needed to do it" and break it in front of the eyes 😉