The EU isn’t a state and has no military or police. As such the EU’s existence is an anecdotal answer to your question in itself: Reliance on (in particular maritime) trade. And yes, China also benefits from trade, but as opposed to democracies (in which the general populace to a greater extent are keys to power) the state does not require trade to sustain itself in the same way.

This makes EU countries more reliable partners for cooperation than China. The same goes for the US from an European perspective, and even with everything going on over there it is still not remotely close.

All states are fundamentally adversaries because they have conflicting interests. To your point however, adversaries do indeed cooperate all the time.