Debian has been a major driver in making many pieces of software reproducible across every distribution; that Debian maintainers so often submit patches upstream and work directly to solve these issues is a big reason for this.

In other words: the work Debian has done absolutely set the stage for this to happen, and it would have taken much longer without them.

In general, Debian aims to upstream the changes they make to software. That allows all other distributions, including Nix, to profit from their work making software reproducible.