But in Lover's Walk, only a few episodes after Angel comes back in bs3, he is already taking on multiple vamps at a time, as are both spike and buffy, in the big 3-versus-gazillion fight where all the vamps are after spike. Which brings us to another question - why is spike always able to fight multiple vampires and demons and kill them without trouble, and then same with angel later on his show. I can buy the monastery thing as a fanwonk explanation for angel being stronger - he had a mission and trained for it. What about spike?
True, but I was referencing Buffy vs. Angel's strength, not Angel vs. Normal vamps. In
Lover's Walk, Angel was stronger than multiple vamps, but much weaker than normal, Buffy out-and-out says so (Angel was still recovering).
Why were Spike & Angel so much stronger? Prior to
Buffy they were two of maybe a dozen legendary Alpha Male Vampires. There are thousands of vampires, yet Angelus, Spike, Nostroyev, Dracula, Prince of Lies, the Master, and Kokistos are the only ones that seem to be the Big Bads of the demon world.
According to Wesley and his Watcher training, Angelus took the top spot on the list of most dangerous with Spike coming in at number two. The Master said that Angelus was the most vicious vampire he'd ever met, which is a big deal coming form him. And Angel managed to kill both Nostroyev & Prince of Lies. Spike used to hunt Slayers, so those guys were never really ordinary vamps.
Why? They never really say, but the popular opinions are because their lineage is more pure since they're both really close to the Master. Also, they were both handpicked to become vamps by Darla & Drusilla who were really discerning about who they sired.