I can't tell if you are saying the market doesn't care if your software is slow, or quoting someone else. Either way it's objectively false and that has been known for decades. Making users wait is a surefire way to make them engage with your product less, and the more you make them wait the less they will use it.

If your boss doesn't care about your software being slow he's incompetent.

https://services.google.com/fh/files/blogs/google_delayexp.p...

https://business.google.com/ca-en/think/marketing-strategies...

https://medium.com/ft-product-technology/a-faster-ft-com-10e...

https://www.pingdom.com/blog/page-load-time-really-affect-bo...