Are you sure? Did you really test this? I guess not...
Yes it is. That's where (since v6) the functionality comes from.
Not even a login works without that endpoint. You really shouldn't skip this in your config.
That's a bit more difficult as internal redirects seem to use absolute and not relative paths. Just simply changing the config will result in a redirect loop:
I don't want to debug that more - just as a hint: See influxDB2.0 alpha - http custom base path · Issue #15721 · influxdata/influxdb · GitHub for a similar problem when putting influxDB to a subpath. There are options in nginx that can rewrite that, but be prepared for some debugging.
I would rather suggest putting pi-hole to a subdomain like http://pi-hole.cnrpi5.example.net/ which would be a no-brainer using my configuration.