The magic he's using are all glamor spells to hide his injuries and heal them. They're not enhancing his strength or abilities in any fashion, especially by the time the story actually catches up to the present. And most importantly he's doing the actual fighting himself. And the reason he keeps needing the healing in the first place is because the city is in hell; the situation was arguably the most dire Angel had seen up to that point, powers or no.Which only further proves my point. It wasn't Angel's human skill that allowed him to fight like that, it was artifacts and spells, things that he didn't have in "I Will Remember You," and probably wouldn't have been able to obtain easily at that point in Los Angeles. Remember, all of his power in "After The Fall" came from things that he salvaged from the Wolfram & Hart offices and the assistance of a very powerful dragon. Once the magic was taken away, he was just plain old badly injured human
Again, Dawn has at least 5 kills under her belt. Dawn. Not Xander or Wood or Riley. Spoiled teenage brat Dawn.
Xander himself dusts multiple vampires in season 1, and saves Buffy's life when Angel could not.