It works both ways. If US left all their long-haul flying to the * partners, it would be completely disadvantageous to them. Instead, each airline offers long hauls where it can generate good revenue and feed it's partners in their hub cities, and vice versa. It's very symbiotic for all parties involved.What does US need more widebodies for in the future, other Star airlines will be more than happy to carry passengers on long-haul sectors. That is why US is in the alliance in the first place, to feed the rest of the alliance.