When running your own backup server, you're forgetting about scenario(however less-likely) when Google Photos will loose your photos, or if your google account gets banned with no ability to call anyone in Google to dispute that. In this case you can safely rely on your own backup to have those files at hand.

I was skeptical about this scenario until one day Gmail lost 1 year worth of my emails. It's just gone. All other emails are there, but not this particular year. And there is no person who you can call to talk about that.