This is true. All new added code is licensed under AGPLv3. But I fail to see how it's the same thing as modifying and open-source tool and re-selling it as a closed source tool. This is what AGPL gives us - anyone can use Pretzel however they want. They can even re-package and re-sell it if they want so long as they too open-source their modifications and improvements.

Selecting the license for an open-source tool backed by a company is tricky. You want your code to be open-source for it's benefits (for eg, for us one benefit is building trust with people working with sensitive data). But, the history of open-source tools is full of tools that another company just started reselling without doing any of the work (sentry, mongodb etc). So, you need to find a balance. AGPLv3 strikes the right balance for us.