The world was united against France, but...
No one wants another major war. It was toward that end that the Partition Treaties were negotiated. Britain was willing to accept France getting Italy, and signed off on it in writing. Spain was a prize to be captured, or divided. Britain/Dutch wanted division, as the best of all options. They were most of the way toward accepting Philip getting all of it, but France forced the general war through bungling diplomacy.
Uniting Spain with another country: This is a constant mantra in alt history, but the reality is that when the WoSS broke out, Philip was third in line, with a younger brother behind him, and his grandfather and father ahead of him. His father was expected to father children, and Philip was at the age of fathering children. There was no push, or expectation, to unite France and Spain. I don't think either wanted it, as it would be untenable. Meanwhile, Karl was second in line to the Austrian throne, with no other male heirs. There was just as much revulsion over the possibility of Spain uniting with Austria as with Spain. Ultimately, with the Bourbon die-off in 1711/12, and Joseph dieing in 1711, all support for Karl ended. In 1700, though, there was more reason to fear uniting with Austria than with France.
France had not really expanded. They kept attempting to, but Louis XIV had the uncanny knack of snatching defeat from the jaws of victory, and only making minimal gains. The 9YW had united the world against France, and more or less stalemated. No one trusted France, for good reason, but had France done its part, only Austria would not have gone along.