I've done modding for Paradox games (never something for the public, but just for myself), and I've done game dev in Godot. I'd say modding of Paradox games like Stellaris is a lot more convenient. There are guides, too, and the lua scripts you will be working with are relatively intuitive in my opinion. Another advantage is, that you may have an easier time to gain an audience and feedback, as it already builds on something that has a lot of people playing it. But that is no guarantee, admittedly.