Now, how does this fit into with how Angel ended?

Um, pretty orthogonally, really. The last season of Angel had a few references to Buffy-and-her-new-Slayer-army, but it didn't have anything to do with the Angel finale.

involved fighting against all odds and probably losing.

As kestrell put it, it was a classic "battle in the pass". Generally, those are holding actions; the Good Guys hope to stave off the enemy from some goal, but not actually survive.