This is totally true, and as such, most humanist claims of ontological superiority over other religions are nonsensical or hypocritical.

I wrote an article about morality recently, and have lately been considering adding a section exploring this called "Secular vs Sectarian Humanism".

The conclusion that I can't escape, the more and more I think about it, is that morality is always subjective: https://medium.com/the-panopticon-publication/morality-is-personal-and-tribal-always-20c8c31f5d29