Isn't that similar to using https://github.com/prometheus/blackbox_exporter with prometheus, alertmanager and grafana?
Beyond just that, the resource usage of Gatus is significantly lower than running Grafana, Prometheus and alertmanager individually - much less running all of them at the same time.
My personal Kubernetes cluster is quite limited in resources after all, and running Prometheus does make that resource pool even smaller than it already is :p
That said, even for clusters that don't have similar resource restrictions, I find that having all of this together in a single application makes it a lot easier to manage, though I guess that's up to the individual :)