webhook.com is open source, and an amazing tool. Could a Russian or Chinese developer basically recreate their service for a different market? Yes, but not without significant work. And then, unless they are as committed to making their product awesome as the webhook.com team is, they'll always be looking over their shoulder. E.g as webhook.com internationalizes, etc.

Is it likely someone would try that in the English-speaking market? I just doubt it. Technology that someone else is using and improving but also made available to you will never be a competitive advantage.