Not your parent, but, to "replace" something means that it fills the same need you have as something else. The trick with talking about this in a generic contex

Not your parent, but, to "replace" something means that it fills the same need you have as something else. The trick with talking about this in a generic context is that some people "need" some things and some do not. Your parent is saying "I do not like Rust and I prefer the GPL, and so this is not equivalent in my eyes." This can be true, while for a different person, simultaneously, "I like Rust and dislike the GPL, and so this is an equivalent in my eyes" can be true as well.