In that case just tell him that those two orbs in casual play groups just plain suck. Usually people get the point. I myself often have “sideboards” in my casual decks that make them a little less casual, for those situations where I need that little bit more oomph. So maybe that’s a way for him to go, leaving them out most games, but bringing them in every now and then, when he had a bad streak or faces some abomination himself.

If your pal is playing Urza and Winter / Static Orb, have a sit down with them and have a serious talk, because Urza + Orbs tends to at least scratch cEDH terrain – it might just be plain too nasty for your table.

On the other hand, Omnath as a green commander has access to a lot of the very best artifact removal – even free ones, like Force of Vigor. So Omnath – even if it is the mono green one – is quite prepared to take on Urza, if it is a more casual build (but casual build and orbs don’t usually mesh that well).

So, yeah, have a sit down and talk sounds like the more correct approach, because playing a tuned Urza at a casual table is just pubstomping.