Like InfoPath, this forum is old. If you use it in Edge set to IE mode, you'll get a toolbar for formatting, and your new lines will be preserved, but I rarely bother with all that..... I agree with you on the one-time scripts. I am not sure what the current state of Muhimbi PDF conversion software is, or whether they still have a product for SharePoint 2010.... But it might be worth exploring. Sometimes the costs of buying a product are less than rolling your own.
If you are moving to SharePoint Online, I would probably migrate my form libraries and use Power Automate for creating the PDFs (again, probably leveraging Muhimbi, or Azure Functions and Logic Apps).
Here's a suggestion for custom script or code approaches from Stack Overflow: https://stackoverflow.com/questions/2006519/automated-conversion-of-infopath-forms-to-pdf
Sorry - I wish I had a direct solution for you! I honestly think your approach sounds fine, except, of course, you'll have to write a bunch of PowerShell scripts :)