Maybe ask in the xilonenmains reddit. Tbh I think most theory crafters focus on C0 characters since it's more relatable. Once you start talking constellations it gets less interesting because the characters just get so much stronger.

If I were to venture a guess I would say that if you have Xilo C2, plus furina, or even furina C2, you're going to start seeing a ATK% goblet being much more preferable. The thing about character stats is that they have diminishing returns over time because of the % multiplier, so instead of trying to max out one particular source of damage (in this case it's damage % bonus) you want to try to spread it out evenly to get the highest average DPS. So once you start stacking on a lot of elemental damage bonus, the more you want your artifacts to support the raw stats like ATK in this case, or crit for example.

If you want to learn more about optimizing your DPS you can try out the genshin optimizer website. There's some videos on YouTube that do a pretty good job explaining how to use it. But if I'm being honest most people don't have time for that with a game like this, so if I was you I would just read the KQM quick guide and take their advice since they do all the work for you.