> Slack-native since that has become the de-facto tool for on-call engineers.

In your particular organization. Slack is one of many instant messaging platforms. Tightly coupling your tool to Slack instead of making it platform agnostic immediately restricts where it can be used.

Other comment threads are already discussing the broader issues with using IM for this job, so I won't go into it here.

Regardless, well done for making something.