Maybe, maybe not. A codebase that hasn't been integrated into your development process and is completely unknown to the development team is as likely to slow down your company as speed it up. At least if you write it from scratch you learn a lot while writing it, you have deep knowledge of how it works, and your team isn't pissed off that they need to suffer through someone else's legacy software.

I've seen plenty of ground up rewrites work, but I have almost never seen legacy software moved to a completely new team successfully.

The other guy seems to believe that the business can survive with a designer and a shopify site. Maybe he's wrong, or maybe the existing customer base and relationships are the real value here and the code is worthless.